UCSD Physics 12

Forms of Energy IIForms of Energy II

Wind Chemical Food Mass-energy LightWind Chemical Food Mass-energy Light

UCSD Physics 12

Spring 2013 2

The Physics 12 Formula ListThe Physics 12 Formula Listbull Lots of forms of energy coming fast and furious Lots of forms of energy coming fast and furious

but to put it in perspective herersquos a list of but to put it in perspective herersquos a list of formulas that yoursquoll need to useformulas that yoursquoll need to use

Relation TypeRelation Type FormulaFormula

Work as force times distanceWork as force times distance WW = = FFdd

Kinetic EnergyKinetic Energy KE = KE = frac12frac12mvmv22

(Grav) Potential Energy(Grav) Potential Energy E = mghE = mgh

Heat ContentHeat Content E = cE = cppmmTT

PowerPower P = P = EEtt

Mass-energyMass-energy E = mcE = mc22

Radiative FluxRadiative Flux F = F = TT44

UCSD Physics 12

Spring 2013 3

Wind EnergyWind Energy

bull Wind can be used as a source of energy (windmills sailing Wind can be used as a source of energy (windmills sailing ships etc)ships etc)

bull Really just kinetic energyReally just kinetic energy

bull Example wind passing through a square meter at 8 meters Example wind passing through a square meter at 8 meters per secondper secondndash Each second we have 8 cubic meters

ndash Air has density of 13 kgm3 so (8 m3)(13 kgm3) = 104 kg of air each second

ndash frac12mv2 = frac12(104 kg)(8 ms)2 = 333 J

ndash 333 J every second 333 Watts of available power per square meter (but to get all of it yoursquod have to stop the wind)

bull Stronger winds Stronger winds more power (like more power (like vv33))Q

UCSD Physics 12

Spring 2013 4

Chemical EnergyChemical Energy

bull Electrostatic energy (associated with charged Electrostatic energy (associated with charged particles like electrons) is stored in the chemical particles like electrons) is stored in the chemical bonds of substances bonds of substances

bull Rearranging these bonds can release energy (some Rearranging these bonds can release energy (some reactions reactions requirerequire energy to be put in) energy to be put in)

bull Typical numbers are 100Typical numbers are 100ndash200 kJ per molendash200 kJ per molendash a mole is 60221023 moleculesparticlesndash typical molecules are tens of grams per moleworks

out to typical numbers like several thousand Joules per gram or a few kilocalories per gram (remember 1 kcal = 4184 J)

UCSD Physics 12

Spring 2013 5

Chemical Energy ExamplesChemical Energy Examples

bull Burning a wooden match releases about one Btu Burning a wooden match releases about one Btu or 1055 Joules (a match is about 03 grams) so or 1055 Joules (a match is about 03 grams) so this is gt3000 Jg nearly 1 kcalgthis is gt3000 Jg nearly 1 kcalg

bull Burning coal releases about 20 kJ per gram of Burning coal releases about 20 kJ per gram of chemical energy or roughly 5 kcalgchemical energy or roughly 5 kcalg

bull Burning gasoline yields about 39 kJ per gram or Burning gasoline yields about 39 kJ per gram or just over 9 kcalgjust over 9 kcalg

bull Very few substances over about 11 kcalgVery few substances over about 11 kcalg

UCSD Physics 12

Spring 2013 6

Energy from FoodEnergy from Food

bull We get the energy to do the things we do out of We get the energy to do the things we do out of food (stored solar energy in the form of chemical food (stored solar energy in the form of chemical energy)energy)

bull Energy sources recognized by our digestive Energy sources recognized by our digestive systemssystemsndash Carbohydrates 4 kilocalories per gram

ndash Proteins 4 kilocalories per gram

ndash Fats 9 kilocalories per gram (like gasoline)

UCSD Physics 12

Spring 2013 7

Nutrition LabelsNutrition Labels

bull Nutrition labels tell you about the Nutrition labels tell you about the energy content of foodenergy content of food

bull Note that capital C means kcalNote that capital C means kcalbull Conversions Conversions Fat 9 kcalgFat 9 kcalg

Carbs 4 kcalgCarbs 4 kcalgProtein 4 kcalgProtein 4 kcalg

bull This product has 72 kcal from fat 48 This product has 72 kcal from fat 48 kcal from carbohydrates and 32 kcal kcal from carbohydrates and 32 kcal from proteinfrom proteinndash sum is 152 kilocalories compare to label

bull 152 kcal = 636 kJ enough to climb 152 kcal = 636 kJ enough to climb about 1000 meters (64 kg person)about 1000 meters (64 kg person)

Q

UCSD Physics 12

Spring 2013 8

Our Human Energy BudgetOur Human Energy Budget

bull A 2000 kcal per day diet A 2000 kcal per day diet means 2000means 20004184 J = 4184 J = 8368000 J per day8368000 J per day

bull 837 MJ837 MJ in (24 hrday) in (24 hrday) (60 minhr)(60 minhr)(60 (60 secmin) = 86400 sec secmin) = 86400 sec corresponds to corresponds to 97 Watts 97 Watts of powerof power

bull Even a couch-potato at Even a couch-potato at 1500 kcalday burns 1500 kcalday burns 75 W75 W

bull More active lifestyles More active lifestyles require greater caloric require greater caloric intake (more energy)intake (more energy)

UCSD Physics 12

Spring 2013 9

Mass-energyMass-energy

bull Einsteinrsquos famous relationEinsteinrsquos famous relationE = mcE = mc22

relates mass to energyrelates mass to energybull In effect they In effect they areare the same thing the same thing

ndash one can be transformed into the otherndash physicists speak generally of mass-energy

bull Seldom experienced in daily life directlySeldom experienced in daily life directlyndash Happens at large scale in the center of the sun and in

nuclear bombs and reactorsndash Actually does happen at barely detectable level in all

energy transactions but the effect is tiny

UCSD Physics 12

Spring 2013 10

E = mcE = mc22 Examples Examples

bull The energy equivalent of one gram of material The energy equivalent of one gram of material ((any compositionany composition) is (0001 kg)) is (0001 kg)(30(30101088 ms) ms)22 = 90= 9010101313 J = 90000000000000 J = 90 TJ J = 90000000000000 J = 90 TJndash Man thatrsquos big

ndash The US energy budget is equivalent to 1000 kgyr

bull If one gram of material undergoes a If one gram of material undergoes a chemical chemical reaction losing about 9000 J of energy how reaction losing about 9000 J of energy how much much massmass does it lose does it lose

9000 J = mc2 so m = 9000c2 = 910391016

= 10-13 kg (would we ever notice)

UCSD Physics 12

Spring 2013 11

Solar Energy is Nuclear Using Solar Energy is Nuclear Using EE = = mcmc22

bull Thermonuclear fusion reactions in the sunrsquos centerThermonuclear fusion reactions in the sunrsquos centerndash Sun is 16 million degrees Celsius in its center

ndash Enough energy to ram protons together (despite mutual repulsion) and make deuterium then helium

ndash Reaction per atom 20 million times more energetic than chemical reactions in general

4 protonsmass = 4029

4He nucleusmass = 40015

2 neutrinos photons (light)

UCSD Physics 12

Spring 2013 12

EE = = mcmc22 in Sun in Sun

bull Helium nucleus is Helium nucleus is lighterlighter than the four protons than the four protonsbull Mass difference is 4029 Mass difference is 4029 40015 = 00276 amu 40015 = 00276 amu

ndash 1 amu (atomic mass unit) is 1660510-27 kg

ndash difference of 45810-29 kg

ndash multiply by c2 to get 41210-12 J

ndash 1 mole (60221023 particles) of protons 251012 J

ndash typical chemical reactions are 100-200 kJmole

ndash nuclear fusion is ~20 million times more potent stuff

Q

UCSD Physics 12

Spring 2013 13

Energy from LightEnergy from Light

bull The tremendous energy from the sun is released as The tremendous energy from the sun is released as light So light carries energylight So light carries energy

bull How muchHow muchbull Best way to get at this is through the process of Best way to get at this is through the process of

ldquoblackbodyrdquo radiation or thermal radiationhellipldquoblackbodyrdquo radiation or thermal radiationhellipbull All objects emit ldquolightrdquoAll objects emit ldquolightrdquo

ndash Though almost all the light we see is reflected light

bull The color and intensity of the emitted radiation The color and intensity of the emitted radiation depend on the objectrsquos temperaturedepend on the objectrsquos temperature

UCSD Physics 12

Spring 2013 14

Emitted Radiationrsquos Color and Intensity Emitted Radiationrsquos Color and Intensity depend on Temperaturedepend on Temperature

Object

YouHeat LampCandle FlameBulb FilamentSunrsquos Surface

Temperature

~ 30 C~ 500 C~ 1700 C~ 2700 C~ 5500 C

Color

Infrared (invisible)Dull redDim orangeYellowBrilliant white

The hotter it gets the ldquobluerrdquo the emitted lightThe hotter it gets the more intense the radiation (more energy)

UCSD Physics 12

Spring 2013 15

ldquoldquoBlackbodyrdquo or Planck SpectrumBlackbodyrdquo or Planck Spectrum

UCSD Physics 12

Spring 2013 16

Same thing on logarithmic scaleSame thing on logarithmic scale

Sun peaks in visible band (05 microns) light bulbs at 1 m we at 10 m(note 0degC = 273degK 300degK = 27degC = 81degF)

UCSD Physics 12

Spring 2013 17

Okay but how much energyOkay but how much energy

bull The power given off of a surface in the form of light is The power given off of a surface in the form of light is proportional to the proportional to the fourth powerfourth power of temperature of temperature

F = F = TT44 in Watts per square meter in Watts per square meterndash the constant is numerically 56710-8 WordmK4m2

ndash easy to remember constant 5678

ndash temperature must be in Kelvinbull ordmK = ordmC + 273

bull ordmC = (59)(ordmF ndash32)

bull Example radiation from your bodyExample radiation from your body(567 10-8) (310)4 = 523 Watts per square meter

(if naked in the cold of space donrsquot let this happen to you)

UCSD Physics 12

Spring 2013 18

Radiant Energy continuedRadiant Energy continued

bull Example The sun is 5800Example The sun is 5800ordmK on its surface soordmK on its surface soF = T4 = (56710-8)(5800)4 = 64107 Wm2

Summing over entire surface area of sun gives 391026 W

bull Compare to total capacity of energy production on Compare to total capacity of energy production on earth 33earth 3310101212 W Wndash Single power plant typically 05ndash10 GW (109 W)

bull In earthly situations radiated power out partially In earthly situations radiated power out partially balanced by radiated power in from other sourcesbalanced by radiated power in from other sourcesndash Not 523 Wm2 in 70ordmF room more like 100 Wm2

bull goes like Th4 ndash Tc

4

Q

UCSD Physics 12

Spring 2013 19

And those are the major playershellipAnd those are the major playershellip

bull Wersquove now seen all the major energy players wersquoll Wersquove now seen all the major energy players wersquoll be discussing in this classbe discussing in this classndash work as force times distance

ndash kinetic energy (wind ocean currents)

ndash gravitational potential energy (hydroelectric tidal)

ndash chemical energy (fossil fuels batteries food biomass)

ndash heat energy (power plants space heating)

ndash mass-energy (nuclear sources sunrsquos energy)

ndash radiant energy (solar energy)

UCSD Physics 12

Spring 2013 20

AssignmentsAssignments

bull Homework 1 due April 12 in classHomework 1 due April 12 in classndash Chapter 1 problems plus online additions

bull see assignments link on web page for details

ndash donrsquot forget to show your workreasoning on the multiple choice

bull the answers alone do not suffice

bull Quiz 1 due Friday April 12 by midnightQuiz 1 due Friday April 12 by midnightndash TED will be up and quizzes available by Thursday

ndash 3 attempts permitted

ndash all numericalquantitative this week

UCSD Physics 12

Spring 2013 2

The Physics 12 Formula ListThe Physics 12 Formula Listbull Lots of forms of energy coming fast and furious Lots of forms of energy coming fast and furious

but to put it in perspective herersquos a list of but to put it in perspective herersquos a list of formulas that yoursquoll need to useformulas that yoursquoll need to use

Relation TypeRelation Type FormulaFormula

Work as force times distanceWork as force times distance WW = = FFdd

Kinetic EnergyKinetic Energy KE = KE = frac12frac12mvmv22

(Grav) Potential Energy(Grav) Potential Energy E = mghE = mgh

Heat ContentHeat Content E = cE = cppmmTT

PowerPower P = P = EEtt

Mass-energyMass-energy E = mcE = mc22

Radiative FluxRadiative Flux F = F = TT44

UCSD Physics 12

Spring 2013 3

Wind EnergyWind Energy

bull Wind can be used as a source of energy (windmills sailing Wind can be used as a source of energy (windmills sailing ships etc)ships etc)

bull Really just kinetic energyReally just kinetic energy

bull Example wind passing through a square meter at 8 meters Example wind passing through a square meter at 8 meters per secondper secondndash Each second we have 8 cubic meters

ndash Air has density of 13 kgm3 so (8 m3)(13 kgm3) = 104 kg of air each second

ndash frac12mv2 = frac12(104 kg)(8 ms)2 = 333 J

ndash 333 J every second 333 Watts of available power per square meter (but to get all of it yoursquod have to stop the wind)

bull Stronger winds Stronger winds more power (like more power (like vv33))Q

UCSD Physics 12

Spring 2013 4

Chemical EnergyChemical Energy

bull Electrostatic energy (associated with charged Electrostatic energy (associated with charged particles like electrons) is stored in the chemical particles like electrons) is stored in the chemical bonds of substances bonds of substances

bull Rearranging these bonds can release energy (some Rearranging these bonds can release energy (some reactions reactions requirerequire energy to be put in) energy to be put in)

bull Typical numbers are 100Typical numbers are 100ndash200 kJ per molendash200 kJ per molendash a mole is 60221023 moleculesparticlesndash typical molecules are tens of grams per moleworks

out to typical numbers like several thousand Joules per gram or a few kilocalories per gram (remember 1 kcal = 4184 J)

UCSD Physics 12

Spring 2013 5

Chemical Energy ExamplesChemical Energy Examples

bull Burning a wooden match releases about one Btu Burning a wooden match releases about one Btu or 1055 Joules (a match is about 03 grams) so or 1055 Joules (a match is about 03 grams) so this is gt3000 Jg nearly 1 kcalgthis is gt3000 Jg nearly 1 kcalg

bull Burning coal releases about 20 kJ per gram of Burning coal releases about 20 kJ per gram of chemical energy or roughly 5 kcalgchemical energy or roughly 5 kcalg

bull Burning gasoline yields about 39 kJ per gram or Burning gasoline yields about 39 kJ per gram or just over 9 kcalgjust over 9 kcalg

bull Very few substances over about 11 kcalgVery few substances over about 11 kcalg

UCSD Physics 12

Spring 2013 6

Energy from FoodEnergy from Food

bull We get the energy to do the things we do out of We get the energy to do the things we do out of food (stored solar energy in the form of chemical food (stored solar energy in the form of chemical energy)energy)

bull Energy sources recognized by our digestive Energy sources recognized by our digestive systemssystemsndash Carbohydrates 4 kilocalories per gram

ndash Proteins 4 kilocalories per gram

ndash Fats 9 kilocalories per gram (like gasoline)

UCSD Physics 12

Spring 2013 7

Nutrition LabelsNutrition Labels

bull Nutrition labels tell you about the Nutrition labels tell you about the energy content of foodenergy content of food

bull Note that capital C means kcalNote that capital C means kcalbull Conversions Conversions Fat 9 kcalgFat 9 kcalg

Carbs 4 kcalgCarbs 4 kcalgProtein 4 kcalgProtein 4 kcalg

bull This product has 72 kcal from fat 48 This product has 72 kcal from fat 48 kcal from carbohydrates and 32 kcal kcal from carbohydrates and 32 kcal from proteinfrom proteinndash sum is 152 kilocalories compare to label

bull 152 kcal = 636 kJ enough to climb 152 kcal = 636 kJ enough to climb about 1000 meters (64 kg person)about 1000 meters (64 kg person)

Q

UCSD Physics 12

Spring 2013 8

Our Human Energy BudgetOur Human Energy Budget

bull A 2000 kcal per day diet A 2000 kcal per day diet means 2000means 20004184 J = 4184 J = 8368000 J per day8368000 J per day

bull 837 MJ837 MJ in (24 hrday) in (24 hrday) (60 minhr)(60 minhr)(60 (60 secmin) = 86400 sec secmin) = 86400 sec corresponds to corresponds to 97 Watts 97 Watts of powerof power

bull Even a couch-potato at Even a couch-potato at 1500 kcalday burns 1500 kcalday burns 75 W75 W

bull More active lifestyles More active lifestyles require greater caloric require greater caloric intake (more energy)intake (more energy)

UCSD Physics 12

Spring 2013 9

Mass-energyMass-energy

bull Einsteinrsquos famous relationEinsteinrsquos famous relationE = mcE = mc22

relates mass to energyrelates mass to energybull In effect they In effect they areare the same thing the same thing

ndash one can be transformed into the otherndash physicists speak generally of mass-energy

bull Seldom experienced in daily life directlySeldom experienced in daily life directlyndash Happens at large scale in the center of the sun and in

nuclear bombs and reactorsndash Actually does happen at barely detectable level in all

energy transactions but the effect is tiny

UCSD Physics 12

Spring 2013 10

E = mcE = mc22 Examples Examples

bull The energy equivalent of one gram of material The energy equivalent of one gram of material ((any compositionany composition) is (0001 kg)) is (0001 kg)(30(30101088 ms) ms)22 = 90= 9010101313 J = 90000000000000 J = 90 TJ J = 90000000000000 J = 90 TJndash Man thatrsquos big

ndash The US energy budget is equivalent to 1000 kgyr

bull If one gram of material undergoes a If one gram of material undergoes a chemical chemical reaction losing about 9000 J of energy how reaction losing about 9000 J of energy how much much massmass does it lose does it lose

9000 J = mc2 so m = 9000c2 = 910391016

= 10-13 kg (would we ever notice)

UCSD Physics 12

Spring 2013 11

Solar Energy is Nuclear Using Solar Energy is Nuclear Using EE = = mcmc22

bull Thermonuclear fusion reactions in the sunrsquos centerThermonuclear fusion reactions in the sunrsquos centerndash Sun is 16 million degrees Celsius in its center

ndash Enough energy to ram protons together (despite mutual repulsion) and make deuterium then helium

ndash Reaction per atom 20 million times more energetic than chemical reactions in general

4 protonsmass = 4029

4He nucleusmass = 40015

2 neutrinos photons (light)

UCSD Physics 12

Spring 2013 12

EE = = mcmc22 in Sun in Sun

bull Helium nucleus is Helium nucleus is lighterlighter than the four protons than the four protonsbull Mass difference is 4029 Mass difference is 4029 40015 = 00276 amu 40015 = 00276 amu

ndash 1 amu (atomic mass unit) is 1660510-27 kg

ndash difference of 45810-29 kg

ndash multiply by c2 to get 41210-12 J

ndash 1 mole (60221023 particles) of protons 251012 J

ndash typical chemical reactions are 100-200 kJmole

ndash nuclear fusion is ~20 million times more potent stuff

Q

UCSD Physics 12

Spring 2013 13

Energy from LightEnergy from Light

bull The tremendous energy from the sun is released as The tremendous energy from the sun is released as light So light carries energylight So light carries energy

bull How muchHow muchbull Best way to get at this is through the process of Best way to get at this is through the process of

ldquoblackbodyrdquo radiation or thermal radiationhellipldquoblackbodyrdquo radiation or thermal radiationhellipbull All objects emit ldquolightrdquoAll objects emit ldquolightrdquo

ndash Though almost all the light we see is reflected light

bull The color and intensity of the emitted radiation The color and intensity of the emitted radiation depend on the objectrsquos temperaturedepend on the objectrsquos temperature

UCSD Physics 12

Spring 2013 14

Emitted Radiationrsquos Color and Intensity Emitted Radiationrsquos Color and Intensity depend on Temperaturedepend on Temperature

Object

YouHeat LampCandle FlameBulb FilamentSunrsquos Surface

Temperature

~ 30 C~ 500 C~ 1700 C~ 2700 C~ 5500 C

Color

Infrared (invisible)Dull redDim orangeYellowBrilliant white

The hotter it gets the ldquobluerrdquo the emitted lightThe hotter it gets the more intense the radiation (more energy)

UCSD Physics 12

Spring 2013 15

ldquoldquoBlackbodyrdquo or Planck SpectrumBlackbodyrdquo or Planck Spectrum

UCSD Physics 12

Spring 2013 16

Same thing on logarithmic scaleSame thing on logarithmic scale

Sun peaks in visible band (05 microns) light bulbs at 1 m we at 10 m(note 0degC = 273degK 300degK = 27degC = 81degF)

UCSD Physics 12

Spring 2013 17

Okay but how much energyOkay but how much energy

bull The power given off of a surface in the form of light is The power given off of a surface in the form of light is proportional to the proportional to the fourth powerfourth power of temperature of temperature

F = F = TT44 in Watts per square meter in Watts per square meterndash the constant is numerically 56710-8 WordmK4m2

ndash easy to remember constant 5678

ndash temperature must be in Kelvinbull ordmK = ordmC + 273

bull ordmC = (59)(ordmF ndash32)

bull Example radiation from your bodyExample radiation from your body(567 10-8) (310)4 = 523 Watts per square meter

(if naked in the cold of space donrsquot let this happen to you)

UCSD Physics 12

Spring 2013 18

Radiant Energy continuedRadiant Energy continued

bull Example The sun is 5800Example The sun is 5800ordmK on its surface soordmK on its surface soF = T4 = (56710-8)(5800)4 = 64107 Wm2

Summing over entire surface area of sun gives 391026 W

bull Compare to total capacity of energy production on Compare to total capacity of energy production on earth 33earth 3310101212 W Wndash Single power plant typically 05ndash10 GW (109 W)

bull In earthly situations radiated power out partially In earthly situations radiated power out partially balanced by radiated power in from other sourcesbalanced by radiated power in from other sourcesndash Not 523 Wm2 in 70ordmF room more like 100 Wm2

bull goes like Th4 ndash Tc

4

Q

UCSD Physics 12

Spring 2013 19

And those are the major playershellipAnd those are the major playershellip

bull Wersquove now seen all the major energy players wersquoll Wersquove now seen all the major energy players wersquoll be discussing in this classbe discussing in this classndash work as force times distance

ndash kinetic energy (wind ocean currents)

ndash gravitational potential energy (hydroelectric tidal)

ndash chemical energy (fossil fuels batteries food biomass)

ndash heat energy (power plants space heating)

ndash mass-energy (nuclear sources sunrsquos energy)

ndash radiant energy (solar energy)

UCSD Physics 12

Spring 2013 20

AssignmentsAssignments

bull Homework 1 due April 12 in classHomework 1 due April 12 in classndash Chapter 1 problems plus online additions

bull see assignments link on web page for details

ndash donrsquot forget to show your workreasoning on the multiple choice

bull the answers alone do not suffice

bull Quiz 1 due Friday April 12 by midnightQuiz 1 due Friday April 12 by midnightndash TED will be up and quizzes available by Thursday

ndash 3 attempts permitted

ndash all numericalquantitative this week

UCSD Physics 12

Spring 2013 3

Wind EnergyWind Energy

bull Wind can be used as a source of energy (windmills sailing Wind can be used as a source of energy (windmills sailing ships etc)ships etc)

bull Really just kinetic energyReally just kinetic energy

bull Example wind passing through a square meter at 8 meters Example wind passing through a square meter at 8 meters per secondper secondndash Each second we have 8 cubic meters

ndash Air has density of 13 kgm3 so (8 m3)(13 kgm3) = 104 kg of air each second

ndash frac12mv2 = frac12(104 kg)(8 ms)2 = 333 J

ndash 333 J every second 333 Watts of available power per square meter (but to get all of it yoursquod have to stop the wind)

bull Stronger winds Stronger winds more power (like more power (like vv33))Q

UCSD Physics 12

Spring 2013 4

Chemical EnergyChemical Energy

bull Electrostatic energy (associated with charged Electrostatic energy (associated with charged particles like electrons) is stored in the chemical particles like electrons) is stored in the chemical bonds of substances bonds of substances

bull Rearranging these bonds can release energy (some Rearranging these bonds can release energy (some reactions reactions requirerequire energy to be put in) energy to be put in)

bull Typical numbers are 100Typical numbers are 100ndash200 kJ per molendash200 kJ per molendash a mole is 60221023 moleculesparticlesndash typical molecules are tens of grams per moleworks

out to typical numbers like several thousand Joules per gram or a few kilocalories per gram (remember 1 kcal = 4184 J)

UCSD Physics 12

Spring 2013 5

Chemical Energy ExamplesChemical Energy Examples

bull Burning a wooden match releases about one Btu Burning a wooden match releases about one Btu or 1055 Joules (a match is about 03 grams) so or 1055 Joules (a match is about 03 grams) so this is gt3000 Jg nearly 1 kcalgthis is gt3000 Jg nearly 1 kcalg

bull Burning coal releases about 20 kJ per gram of Burning coal releases about 20 kJ per gram of chemical energy or roughly 5 kcalgchemical energy or roughly 5 kcalg

bull Burning gasoline yields about 39 kJ per gram or Burning gasoline yields about 39 kJ per gram or just over 9 kcalgjust over 9 kcalg

bull Very few substances over about 11 kcalgVery few substances over about 11 kcalg

UCSD Physics 12

Spring 2013 6

Energy from FoodEnergy from Food

bull We get the energy to do the things we do out of We get the energy to do the things we do out of food (stored solar energy in the form of chemical food (stored solar energy in the form of chemical energy)energy)

bull Energy sources recognized by our digestive Energy sources recognized by our digestive systemssystemsndash Carbohydrates 4 kilocalories per gram

ndash Proteins 4 kilocalories per gram

ndash Fats 9 kilocalories per gram (like gasoline)

UCSD Physics 12

Spring 2013 7

Nutrition LabelsNutrition Labels

bull Nutrition labels tell you about the Nutrition labels tell you about the energy content of foodenergy content of food

bull Note that capital C means kcalNote that capital C means kcalbull Conversions Conversions Fat 9 kcalgFat 9 kcalg

Carbs 4 kcalgCarbs 4 kcalgProtein 4 kcalgProtein 4 kcalg

bull This product has 72 kcal from fat 48 This product has 72 kcal from fat 48 kcal from carbohydrates and 32 kcal kcal from carbohydrates and 32 kcal from proteinfrom proteinndash sum is 152 kilocalories compare to label

bull 152 kcal = 636 kJ enough to climb 152 kcal = 636 kJ enough to climb about 1000 meters (64 kg person)about 1000 meters (64 kg person)

Q

UCSD Physics 12

Spring 2013 8

Our Human Energy BudgetOur Human Energy Budget

bull A 2000 kcal per day diet A 2000 kcal per day diet means 2000means 20004184 J = 4184 J = 8368000 J per day8368000 J per day

bull 837 MJ837 MJ in (24 hrday) in (24 hrday) (60 minhr)(60 minhr)(60 (60 secmin) = 86400 sec secmin) = 86400 sec corresponds to corresponds to 97 Watts 97 Watts of powerof power

bull Even a couch-potato at Even a couch-potato at 1500 kcalday burns 1500 kcalday burns 75 W75 W

bull More active lifestyles More active lifestyles require greater caloric require greater caloric intake (more energy)intake (more energy)

UCSD Physics 12

Spring 2013 9

Mass-energyMass-energy

bull Einsteinrsquos famous relationEinsteinrsquos famous relationE = mcE = mc22

relates mass to energyrelates mass to energybull In effect they In effect they areare the same thing the same thing

ndash one can be transformed into the otherndash physicists speak generally of mass-energy

bull Seldom experienced in daily life directlySeldom experienced in daily life directlyndash Happens at large scale in the center of the sun and in

nuclear bombs and reactorsndash Actually does happen at barely detectable level in all

energy transactions but the effect is tiny

UCSD Physics 12

Spring 2013 10

E = mcE = mc22 Examples Examples

bull The energy equivalent of one gram of material The energy equivalent of one gram of material ((any compositionany composition) is (0001 kg)) is (0001 kg)(30(30101088 ms) ms)22 = 90= 9010101313 J = 90000000000000 J = 90 TJ J = 90000000000000 J = 90 TJndash Man thatrsquos big

ndash The US energy budget is equivalent to 1000 kgyr

bull If one gram of material undergoes a If one gram of material undergoes a chemical chemical reaction losing about 9000 J of energy how reaction losing about 9000 J of energy how much much massmass does it lose does it lose

9000 J = mc2 so m = 9000c2 = 910391016

= 10-13 kg (would we ever notice)

UCSD Physics 12

Spring 2013 11

Solar Energy is Nuclear Using Solar Energy is Nuclear Using EE = = mcmc22

bull Thermonuclear fusion reactions in the sunrsquos centerThermonuclear fusion reactions in the sunrsquos centerndash Sun is 16 million degrees Celsius in its center

ndash Enough energy to ram protons together (despite mutual repulsion) and make deuterium then helium

ndash Reaction per atom 20 million times more energetic than chemical reactions in general

4 protonsmass = 4029

4He nucleusmass = 40015

2 neutrinos photons (light)

UCSD Physics 12

Spring 2013 12

EE = = mcmc22 in Sun in Sun

bull Helium nucleus is Helium nucleus is lighterlighter than the four protons than the four protonsbull Mass difference is 4029 Mass difference is 4029 40015 = 00276 amu 40015 = 00276 amu

ndash 1 amu (atomic mass unit) is 1660510-27 kg

ndash difference of 45810-29 kg

ndash multiply by c2 to get 41210-12 J

ndash 1 mole (60221023 particles) of protons 251012 J

ndash typical chemical reactions are 100-200 kJmole

ndash nuclear fusion is ~20 million times more potent stuff

Q

UCSD Physics 12

Spring 2013 13

Energy from LightEnergy from Light

bull The tremendous energy from the sun is released as The tremendous energy from the sun is released as light So light carries energylight So light carries energy

bull How muchHow muchbull Best way to get at this is through the process of Best way to get at this is through the process of

ldquoblackbodyrdquo radiation or thermal radiationhellipldquoblackbodyrdquo radiation or thermal radiationhellipbull All objects emit ldquolightrdquoAll objects emit ldquolightrdquo

ndash Though almost all the light we see is reflected light

bull The color and intensity of the emitted radiation The color and intensity of the emitted radiation depend on the objectrsquos temperaturedepend on the objectrsquos temperature

UCSD Physics 12

Spring 2013 14

Emitted Radiationrsquos Color and Intensity Emitted Radiationrsquos Color and Intensity depend on Temperaturedepend on Temperature

Object

YouHeat LampCandle FlameBulb FilamentSunrsquos Surface

Temperature

~ 30 C~ 500 C~ 1700 C~ 2700 C~ 5500 C

Color

Infrared (invisible)Dull redDim orangeYellowBrilliant white

The hotter it gets the ldquobluerrdquo the emitted lightThe hotter it gets the more intense the radiation (more energy)

UCSD Physics 12

Spring 2013 15

ldquoldquoBlackbodyrdquo or Planck SpectrumBlackbodyrdquo or Planck Spectrum

UCSD Physics 12

Spring 2013 16

Same thing on logarithmic scaleSame thing on logarithmic scale

Sun peaks in visible band (05 microns) light bulbs at 1 m we at 10 m(note 0degC = 273degK 300degK = 27degC = 81degF)

UCSD Physics 12

Spring 2013 17

Okay but how much energyOkay but how much energy

bull The power given off of a surface in the form of light is The power given off of a surface in the form of light is proportional to the proportional to the fourth powerfourth power of temperature of temperature

F = F = TT44 in Watts per square meter in Watts per square meterndash the constant is numerically 56710-8 WordmK4m2

ndash easy to remember constant 5678

ndash temperature must be in Kelvinbull ordmK = ordmC + 273

bull ordmC = (59)(ordmF ndash32)

bull Example radiation from your bodyExample radiation from your body(567 10-8) (310)4 = 523 Watts per square meter

(if naked in the cold of space donrsquot let this happen to you)

UCSD Physics 12

Spring 2013 18

Radiant Energy continuedRadiant Energy continued

bull Example The sun is 5800Example The sun is 5800ordmK on its surface soordmK on its surface soF = T4 = (56710-8)(5800)4 = 64107 Wm2

Summing over entire surface area of sun gives 391026 W

bull Compare to total capacity of energy production on Compare to total capacity of energy production on earth 33earth 3310101212 W Wndash Single power plant typically 05ndash10 GW (109 W)

bull In earthly situations radiated power out partially In earthly situations radiated power out partially balanced by radiated power in from other sourcesbalanced by radiated power in from other sourcesndash Not 523 Wm2 in 70ordmF room more like 100 Wm2

bull goes like Th4 ndash Tc

4

Q

UCSD Physics 12

Spring 2013 19

And those are the major playershellipAnd those are the major playershellip

bull Wersquove now seen all the major energy players wersquoll Wersquove now seen all the major energy players wersquoll be discussing in this classbe discussing in this classndash work as force times distance

ndash kinetic energy (wind ocean currents)

ndash gravitational potential energy (hydroelectric tidal)

ndash chemical energy (fossil fuels batteries food biomass)

ndash heat energy (power plants space heating)

ndash mass-energy (nuclear sources sunrsquos energy)

ndash radiant energy (solar energy)

UCSD Physics 12

Spring 2013 20

AssignmentsAssignments

bull Homework 1 due April 12 in classHomework 1 due April 12 in classndash Chapter 1 problems plus online additions

bull see assignments link on web page for details

ndash donrsquot forget to show your workreasoning on the multiple choice

bull the answers alone do not suffice

bull Quiz 1 due Friday April 12 by midnightQuiz 1 due Friday April 12 by midnightndash TED will be up and quizzes available by Thursday

ndash 3 attempts permitted

ndash all numericalquantitative this week

UCSD Physics 12

Spring 2013 4

Chemical EnergyChemical Energy

bull Electrostatic energy (associated with charged Electrostatic energy (associated with charged particles like electrons) is stored in the chemical particles like electrons) is stored in the chemical bonds of substances bonds of substances

bull Rearranging these bonds can release energy (some Rearranging these bonds can release energy (some reactions reactions requirerequire energy to be put in) energy to be put in)

bull Typical numbers are 100Typical numbers are 100ndash200 kJ per molendash200 kJ per molendash a mole is 60221023 moleculesparticlesndash typical molecules are tens of grams per moleworks

out to typical numbers like several thousand Joules per gram or a few kilocalories per gram (remember 1 kcal = 4184 J)

UCSD Physics 12

Spring 2013 5

Chemical Energy ExamplesChemical Energy Examples

bull Burning a wooden match releases about one Btu Burning a wooden match releases about one Btu or 1055 Joules (a match is about 03 grams) so or 1055 Joules (a match is about 03 grams) so this is gt3000 Jg nearly 1 kcalgthis is gt3000 Jg nearly 1 kcalg

bull Burning coal releases about 20 kJ per gram of Burning coal releases about 20 kJ per gram of chemical energy or roughly 5 kcalgchemical energy or roughly 5 kcalg

bull Burning gasoline yields about 39 kJ per gram or Burning gasoline yields about 39 kJ per gram or just over 9 kcalgjust over 9 kcalg

bull Very few substances over about 11 kcalgVery few substances over about 11 kcalg

UCSD Physics 12

Spring 2013 6

Energy from FoodEnergy from Food

bull We get the energy to do the things we do out of We get the energy to do the things we do out of food (stored solar energy in the form of chemical food (stored solar energy in the form of chemical energy)energy)

bull Energy sources recognized by our digestive Energy sources recognized by our digestive systemssystemsndash Carbohydrates 4 kilocalories per gram

ndash Proteins 4 kilocalories per gram

ndash Fats 9 kilocalories per gram (like gasoline)

UCSD Physics 12

Spring 2013 7

Nutrition LabelsNutrition Labels

bull Nutrition labels tell you about the Nutrition labels tell you about the energy content of foodenergy content of food

bull Note that capital C means kcalNote that capital C means kcalbull Conversions Conversions Fat 9 kcalgFat 9 kcalg

Carbs 4 kcalgCarbs 4 kcalgProtein 4 kcalgProtein 4 kcalg

bull This product has 72 kcal from fat 48 This product has 72 kcal from fat 48 kcal from carbohydrates and 32 kcal kcal from carbohydrates and 32 kcal from proteinfrom proteinndash sum is 152 kilocalories compare to label

bull 152 kcal = 636 kJ enough to climb 152 kcal = 636 kJ enough to climb about 1000 meters (64 kg person)about 1000 meters (64 kg person)

Q

UCSD Physics 12

Spring 2013 8

Our Human Energy BudgetOur Human Energy Budget

bull A 2000 kcal per day diet A 2000 kcal per day diet means 2000means 20004184 J = 4184 J = 8368000 J per day8368000 J per day

bull 837 MJ837 MJ in (24 hrday) in (24 hrday) (60 minhr)(60 minhr)(60 (60 secmin) = 86400 sec secmin) = 86400 sec corresponds to corresponds to 97 Watts 97 Watts of powerof power

bull Even a couch-potato at Even a couch-potato at 1500 kcalday burns 1500 kcalday burns 75 W75 W

bull More active lifestyles More active lifestyles require greater caloric require greater caloric intake (more energy)intake (more energy)

UCSD Physics 12

Spring 2013 9

Mass-energyMass-energy

bull Einsteinrsquos famous relationEinsteinrsquos famous relationE = mcE = mc22

relates mass to energyrelates mass to energybull In effect they In effect they areare the same thing the same thing

ndash one can be transformed into the otherndash physicists speak generally of mass-energy

bull Seldom experienced in daily life directlySeldom experienced in daily life directlyndash Happens at large scale in the center of the sun and in

nuclear bombs and reactorsndash Actually does happen at barely detectable level in all

energy transactions but the effect is tiny

UCSD Physics 12

Spring 2013 10

E = mcE = mc22 Examples Examples

bull The energy equivalent of one gram of material The energy equivalent of one gram of material ((any compositionany composition) is (0001 kg)) is (0001 kg)(30(30101088 ms) ms)22 = 90= 9010101313 J = 90000000000000 J = 90 TJ J = 90000000000000 J = 90 TJndash Man thatrsquos big

ndash The US energy budget is equivalent to 1000 kgyr

bull If one gram of material undergoes a If one gram of material undergoes a chemical chemical reaction losing about 9000 J of energy how reaction losing about 9000 J of energy how much much massmass does it lose does it lose

9000 J = mc2 so m = 9000c2 = 910391016

= 10-13 kg (would we ever notice)

UCSD Physics 12

Spring 2013 11

Solar Energy is Nuclear Using Solar Energy is Nuclear Using EE = = mcmc22

bull Thermonuclear fusion reactions in the sunrsquos centerThermonuclear fusion reactions in the sunrsquos centerndash Sun is 16 million degrees Celsius in its center

ndash Enough energy to ram protons together (despite mutual repulsion) and make deuterium then helium

ndash Reaction per atom 20 million times more energetic than chemical reactions in general

4 protonsmass = 4029

4He nucleusmass = 40015

2 neutrinos photons (light)

UCSD Physics 12

Spring 2013 12

EE = = mcmc22 in Sun in Sun

bull Helium nucleus is Helium nucleus is lighterlighter than the four protons than the four protonsbull Mass difference is 4029 Mass difference is 4029 40015 = 00276 amu 40015 = 00276 amu

ndash 1 amu (atomic mass unit) is 1660510-27 kg

ndash difference of 45810-29 kg

ndash multiply by c2 to get 41210-12 J

ndash 1 mole (60221023 particles) of protons 251012 J

ndash typical chemical reactions are 100-200 kJmole

ndash nuclear fusion is ~20 million times more potent stuff

Q

UCSD Physics 12

Spring 2013 13

Energy from LightEnergy from Light

bull The tremendous energy from the sun is released as The tremendous energy from the sun is released as light So light carries energylight So light carries energy

bull How muchHow muchbull Best way to get at this is through the process of Best way to get at this is through the process of

ldquoblackbodyrdquo radiation or thermal radiationhellipldquoblackbodyrdquo radiation or thermal radiationhellipbull All objects emit ldquolightrdquoAll objects emit ldquolightrdquo

ndash Though almost all the light we see is reflected light

bull The color and intensity of the emitted radiation The color and intensity of the emitted radiation depend on the objectrsquos temperaturedepend on the objectrsquos temperature

UCSD Physics 12

Spring 2013 14

Emitted Radiationrsquos Color and Intensity Emitted Radiationrsquos Color and Intensity depend on Temperaturedepend on Temperature

Object

YouHeat LampCandle FlameBulb FilamentSunrsquos Surface

Temperature

~ 30 C~ 500 C~ 1700 C~ 2700 C~ 5500 C

Color

Infrared (invisible)Dull redDim orangeYellowBrilliant white

The hotter it gets the ldquobluerrdquo the emitted lightThe hotter it gets the more intense the radiation (more energy)

UCSD Physics 12

Spring 2013 15

ldquoldquoBlackbodyrdquo or Planck SpectrumBlackbodyrdquo or Planck Spectrum

UCSD Physics 12

Spring 2013 16

Same thing on logarithmic scaleSame thing on logarithmic scale

Sun peaks in visible band (05 microns) light bulbs at 1 m we at 10 m(note 0degC = 273degK 300degK = 27degC = 81degF)

UCSD Physics 12

Spring 2013 17

Okay but how much energyOkay but how much energy

bull The power given off of a surface in the form of light is The power given off of a surface in the form of light is proportional to the proportional to the fourth powerfourth power of temperature of temperature

F = F = TT44 in Watts per square meter in Watts per square meterndash the constant is numerically 56710-8 WordmK4m2

ndash easy to remember constant 5678

ndash temperature must be in Kelvinbull ordmK = ordmC + 273

bull ordmC = (59)(ordmF ndash32)

bull Example radiation from your bodyExample radiation from your body(567 10-8) (310)4 = 523 Watts per square meter

(if naked in the cold of space donrsquot let this happen to you)

UCSD Physics 12

Spring 2013 18

Radiant Energy continuedRadiant Energy continued

bull Example The sun is 5800Example The sun is 5800ordmK on its surface soordmK on its surface soF = T4 = (56710-8)(5800)4 = 64107 Wm2

Summing over entire surface area of sun gives 391026 W

bull Compare to total capacity of energy production on Compare to total capacity of energy production on earth 33earth 3310101212 W Wndash Single power plant typically 05ndash10 GW (109 W)

bull In earthly situations radiated power out partially In earthly situations radiated power out partially balanced by radiated power in from other sourcesbalanced by radiated power in from other sourcesndash Not 523 Wm2 in 70ordmF room more like 100 Wm2

bull goes like Th4 ndash Tc

4

Q

UCSD Physics 12

Spring 2013 19

And those are the major playershellipAnd those are the major playershellip

bull Wersquove now seen all the major energy players wersquoll Wersquove now seen all the major energy players wersquoll be discussing in this classbe discussing in this classndash work as force times distance

ndash kinetic energy (wind ocean currents)

ndash gravitational potential energy (hydroelectric tidal)

ndash chemical energy (fossil fuels batteries food biomass)

ndash heat energy (power plants space heating)

ndash mass-energy (nuclear sources sunrsquos energy)

ndash radiant energy (solar energy)

UCSD Physics 12

Spring 2013 20

AssignmentsAssignments

bull Homework 1 due April 12 in classHomework 1 due April 12 in classndash Chapter 1 problems plus online additions

bull see assignments link on web page for details

ndash donrsquot forget to show your workreasoning on the multiple choice

bull the answers alone do not suffice

bull Quiz 1 due Friday April 12 by midnightQuiz 1 due Friday April 12 by midnightndash TED will be up and quizzes available by Thursday

ndash 3 attempts permitted

ndash all numericalquantitative this week

UCSD Physics 12

Spring 2013 5

Chemical Energy ExamplesChemical Energy Examples

bull Burning a wooden match releases about one Btu Burning a wooden match releases about one Btu or 1055 Joules (a match is about 03 grams) so or 1055 Joules (a match is about 03 grams) so this is gt3000 Jg nearly 1 kcalgthis is gt3000 Jg nearly 1 kcalg

bull Burning coal releases about 20 kJ per gram of Burning coal releases about 20 kJ per gram of chemical energy or roughly 5 kcalgchemical energy or roughly 5 kcalg

bull Burning gasoline yields about 39 kJ per gram or Burning gasoline yields about 39 kJ per gram or just over 9 kcalgjust over 9 kcalg

bull Very few substances over about 11 kcalgVery few substances over about 11 kcalg

UCSD Physics 12

Spring 2013 6

Energy from FoodEnergy from Food

bull We get the energy to do the things we do out of We get the energy to do the things we do out of food (stored solar energy in the form of chemical food (stored solar energy in the form of chemical energy)energy)

bull Energy sources recognized by our digestive Energy sources recognized by our digestive systemssystemsndash Carbohydrates 4 kilocalories per gram

ndash Proteins 4 kilocalories per gram

ndash Fats 9 kilocalories per gram (like gasoline)

UCSD Physics 12

Spring 2013 7

Nutrition LabelsNutrition Labels

bull Nutrition labels tell you about the Nutrition labels tell you about the energy content of foodenergy content of food

bull Note that capital C means kcalNote that capital C means kcalbull Conversions Conversions Fat 9 kcalgFat 9 kcalg

Carbs 4 kcalgCarbs 4 kcalgProtein 4 kcalgProtein 4 kcalg

bull This product has 72 kcal from fat 48 This product has 72 kcal from fat 48 kcal from carbohydrates and 32 kcal kcal from carbohydrates and 32 kcal from proteinfrom proteinndash sum is 152 kilocalories compare to label

bull 152 kcal = 636 kJ enough to climb 152 kcal = 636 kJ enough to climb about 1000 meters (64 kg person)about 1000 meters (64 kg person)

Q

UCSD Physics 12

Spring 2013 8

Our Human Energy BudgetOur Human Energy Budget

bull A 2000 kcal per day diet A 2000 kcal per day diet means 2000means 20004184 J = 4184 J = 8368000 J per day8368000 J per day

bull 837 MJ837 MJ in (24 hrday) in (24 hrday) (60 minhr)(60 minhr)(60 (60 secmin) = 86400 sec secmin) = 86400 sec corresponds to corresponds to 97 Watts 97 Watts of powerof power

bull Even a couch-potato at Even a couch-potato at 1500 kcalday burns 1500 kcalday burns 75 W75 W

bull More active lifestyles More active lifestyles require greater caloric require greater caloric intake (more energy)intake (more energy)

UCSD Physics 12

Spring 2013 9

Mass-energyMass-energy

bull Einsteinrsquos famous relationEinsteinrsquos famous relationE = mcE = mc22

relates mass to energyrelates mass to energybull In effect they In effect they areare the same thing the same thing

ndash one can be transformed into the otherndash physicists speak generally of mass-energy

bull Seldom experienced in daily life directlySeldom experienced in daily life directlyndash Happens at large scale in the center of the sun and in

nuclear bombs and reactorsndash Actually does happen at barely detectable level in all

energy transactions but the effect is tiny

UCSD Physics 12

Spring 2013 10

E = mcE = mc22 Examples Examples

bull The energy equivalent of one gram of material The energy equivalent of one gram of material ((any compositionany composition) is (0001 kg)) is (0001 kg)(30(30101088 ms) ms)22 = 90= 9010101313 J = 90000000000000 J = 90 TJ J = 90000000000000 J = 90 TJndash Man thatrsquos big

ndash The US energy budget is equivalent to 1000 kgyr

bull If one gram of material undergoes a If one gram of material undergoes a chemical chemical reaction losing about 9000 J of energy how reaction losing about 9000 J of energy how much much massmass does it lose does it lose

9000 J = mc2 so m = 9000c2 = 910391016

= 10-13 kg (would we ever notice)

UCSD Physics 12

Spring 2013 11

Solar Energy is Nuclear Using Solar Energy is Nuclear Using EE = = mcmc22

bull Thermonuclear fusion reactions in the sunrsquos centerThermonuclear fusion reactions in the sunrsquos centerndash Sun is 16 million degrees Celsius in its center

ndash Enough energy to ram protons together (despite mutual repulsion) and make deuterium then helium

ndash Reaction per atom 20 million times more energetic than chemical reactions in general

4 protonsmass = 4029

4He nucleusmass = 40015

2 neutrinos photons (light)

UCSD Physics 12

Spring 2013 12

EE = = mcmc22 in Sun in Sun

bull Helium nucleus is Helium nucleus is lighterlighter than the four protons than the four protonsbull Mass difference is 4029 Mass difference is 4029 40015 = 00276 amu 40015 = 00276 amu

ndash 1 amu (atomic mass unit) is 1660510-27 kg

ndash difference of 45810-29 kg

ndash multiply by c2 to get 41210-12 J

ndash 1 mole (60221023 particles) of protons 251012 J

ndash typical chemical reactions are 100-200 kJmole

ndash nuclear fusion is ~20 million times more potent stuff

Q

UCSD Physics 12

Spring 2013 13

Energy from LightEnergy from Light

bull The tremendous energy from the sun is released as The tremendous energy from the sun is released as light So light carries energylight So light carries energy

bull How muchHow muchbull Best way to get at this is through the process of Best way to get at this is through the process of

ldquoblackbodyrdquo radiation or thermal radiationhellipldquoblackbodyrdquo radiation or thermal radiationhellipbull All objects emit ldquolightrdquoAll objects emit ldquolightrdquo

ndash Though almost all the light we see is reflected light

bull The color and intensity of the emitted radiation The color and intensity of the emitted radiation depend on the objectrsquos temperaturedepend on the objectrsquos temperature

UCSD Physics 12

Spring 2013 14

Emitted Radiationrsquos Color and Intensity Emitted Radiationrsquos Color and Intensity depend on Temperaturedepend on Temperature

Object

YouHeat LampCandle FlameBulb FilamentSunrsquos Surface

Temperature

~ 30 C~ 500 C~ 1700 C~ 2700 C~ 5500 C

Color

Infrared (invisible)Dull redDim orangeYellowBrilliant white

The hotter it gets the ldquobluerrdquo the emitted lightThe hotter it gets the more intense the radiation (more energy)

UCSD Physics 12

Spring 2013 15

ldquoldquoBlackbodyrdquo or Planck SpectrumBlackbodyrdquo or Planck Spectrum

UCSD Physics 12

Spring 2013 16

Same thing on logarithmic scaleSame thing on logarithmic scale

Sun peaks in visible band (05 microns) light bulbs at 1 m we at 10 m(note 0degC = 273degK 300degK = 27degC = 81degF)

UCSD Physics 12

Spring 2013 17

Okay but how much energyOkay but how much energy

bull The power given off of a surface in the form of light is The power given off of a surface in the form of light is proportional to the proportional to the fourth powerfourth power of temperature of temperature

F = F = TT44 in Watts per square meter in Watts per square meterndash the constant is numerically 56710-8 WordmK4m2

ndash easy to remember constant 5678

ndash temperature must be in Kelvinbull ordmK = ordmC + 273

bull ordmC = (59)(ordmF ndash32)

bull Example radiation from your bodyExample radiation from your body(567 10-8) (310)4 = 523 Watts per square meter

(if naked in the cold of space donrsquot let this happen to you)

UCSD Physics 12

Spring 2013 18

Radiant Energy continuedRadiant Energy continued

bull Example The sun is 5800Example The sun is 5800ordmK on its surface soordmK on its surface soF = T4 = (56710-8)(5800)4 = 64107 Wm2

Summing over entire surface area of sun gives 391026 W

bull Compare to total capacity of energy production on Compare to total capacity of energy production on earth 33earth 3310101212 W Wndash Single power plant typically 05ndash10 GW (109 W)

bull In earthly situations radiated power out partially In earthly situations radiated power out partially balanced by radiated power in from other sourcesbalanced by radiated power in from other sourcesndash Not 523 Wm2 in 70ordmF room more like 100 Wm2

bull goes like Th4 ndash Tc

4

Q

UCSD Physics 12

Spring 2013 19

And those are the major playershellipAnd those are the major playershellip

bull Wersquove now seen all the major energy players wersquoll Wersquove now seen all the major energy players wersquoll be discussing in this classbe discussing in this classndash work as force times distance

ndash kinetic energy (wind ocean currents)

ndash gravitational potential energy (hydroelectric tidal)

ndash chemical energy (fossil fuels batteries food biomass)

ndash heat energy (power plants space heating)

ndash mass-energy (nuclear sources sunrsquos energy)

ndash radiant energy (solar energy)

UCSD Physics 12

Spring 2013 20

AssignmentsAssignments

bull Homework 1 due April 12 in classHomework 1 due April 12 in classndash Chapter 1 problems plus online additions

bull see assignments link on web page for details

ndash donrsquot forget to show your workreasoning on the multiple choice

bull the answers alone do not suffice

bull Quiz 1 due Friday April 12 by midnightQuiz 1 due Friday April 12 by midnightndash TED will be up and quizzes available by Thursday

ndash 3 attempts permitted

ndash all numericalquantitative this week

UCSD Physics 12

Spring 2013 6

Energy from FoodEnergy from Food

bull We get the energy to do the things we do out of We get the energy to do the things we do out of food (stored solar energy in the form of chemical food (stored solar energy in the form of chemical energy)energy)

bull Energy sources recognized by our digestive Energy sources recognized by our digestive systemssystemsndash Carbohydrates 4 kilocalories per gram

ndash Proteins 4 kilocalories per gram

ndash Fats 9 kilocalories per gram (like gasoline)

UCSD Physics 12

Spring 2013 7

Nutrition LabelsNutrition Labels

bull Nutrition labels tell you about the Nutrition labels tell you about the energy content of foodenergy content of food

bull Note that capital C means kcalNote that capital C means kcalbull Conversions Conversions Fat 9 kcalgFat 9 kcalg

Carbs 4 kcalgCarbs 4 kcalgProtein 4 kcalgProtein 4 kcalg

bull This product has 72 kcal from fat 48 This product has 72 kcal from fat 48 kcal from carbohydrates and 32 kcal kcal from carbohydrates and 32 kcal from proteinfrom proteinndash sum is 152 kilocalories compare to label

bull 152 kcal = 636 kJ enough to climb 152 kcal = 636 kJ enough to climb about 1000 meters (64 kg person)about 1000 meters (64 kg person)

Q

UCSD Physics 12

Spring 2013 8

Our Human Energy BudgetOur Human Energy Budget

bull A 2000 kcal per day diet A 2000 kcal per day diet means 2000means 20004184 J = 4184 J = 8368000 J per day8368000 J per day

bull 837 MJ837 MJ in (24 hrday) in (24 hrday) (60 minhr)(60 minhr)(60 (60 secmin) = 86400 sec secmin) = 86400 sec corresponds to corresponds to 97 Watts 97 Watts of powerof power

bull Even a couch-potato at Even a couch-potato at 1500 kcalday burns 1500 kcalday burns 75 W75 W

bull More active lifestyles More active lifestyles require greater caloric require greater caloric intake (more energy)intake (more energy)

UCSD Physics 12

Spring 2013 9

Mass-energyMass-energy

bull Einsteinrsquos famous relationEinsteinrsquos famous relationE = mcE = mc22

relates mass to energyrelates mass to energybull In effect they In effect they areare the same thing the same thing

ndash one can be transformed into the otherndash physicists speak generally of mass-energy

bull Seldom experienced in daily life directlySeldom experienced in daily life directlyndash Happens at large scale in the center of the sun and in

nuclear bombs and reactorsndash Actually does happen at barely detectable level in all

energy transactions but the effect is tiny

UCSD Physics 12

Spring 2013 10

E = mcE = mc22 Examples Examples

bull The energy equivalent of one gram of material The energy equivalent of one gram of material ((any compositionany composition) is (0001 kg)) is (0001 kg)(30(30101088 ms) ms)22 = 90= 9010101313 J = 90000000000000 J = 90 TJ J = 90000000000000 J = 90 TJndash Man thatrsquos big

ndash The US energy budget is equivalent to 1000 kgyr

bull If one gram of material undergoes a If one gram of material undergoes a chemical chemical reaction losing about 9000 J of energy how reaction losing about 9000 J of energy how much much massmass does it lose does it lose

9000 J = mc2 so m = 9000c2 = 910391016

= 10-13 kg (would we ever notice)

UCSD Physics 12

Spring 2013 11

Solar Energy is Nuclear Using Solar Energy is Nuclear Using EE = = mcmc22

bull Thermonuclear fusion reactions in the sunrsquos centerThermonuclear fusion reactions in the sunrsquos centerndash Sun is 16 million degrees Celsius in its center

ndash Enough energy to ram protons together (despite mutual repulsion) and make deuterium then helium

ndash Reaction per atom 20 million times more energetic than chemical reactions in general

4 protonsmass = 4029

4He nucleusmass = 40015

2 neutrinos photons (light)

UCSD Physics 12

Spring 2013 12

EE = = mcmc22 in Sun in Sun

bull Helium nucleus is Helium nucleus is lighterlighter than the four protons than the four protonsbull Mass difference is 4029 Mass difference is 4029 40015 = 00276 amu 40015 = 00276 amu

ndash 1 amu (atomic mass unit) is 1660510-27 kg

ndash difference of 45810-29 kg

ndash multiply by c2 to get 41210-12 J

ndash 1 mole (60221023 particles) of protons 251012 J

ndash typical chemical reactions are 100-200 kJmole

ndash nuclear fusion is ~20 million times more potent stuff

Q

UCSD Physics 12

Spring 2013 13

Energy from LightEnergy from Light

bull The tremendous energy from the sun is released as The tremendous energy from the sun is released as light So light carries energylight So light carries energy

bull How muchHow muchbull Best way to get at this is through the process of Best way to get at this is through the process of

ldquoblackbodyrdquo radiation or thermal radiationhellipldquoblackbodyrdquo radiation or thermal radiationhellipbull All objects emit ldquolightrdquoAll objects emit ldquolightrdquo

ndash Though almost all the light we see is reflected light

bull The color and intensity of the emitted radiation The color and intensity of the emitted radiation depend on the objectrsquos temperaturedepend on the objectrsquos temperature

UCSD Physics 12

Spring 2013 14

Emitted Radiationrsquos Color and Intensity Emitted Radiationrsquos Color and Intensity depend on Temperaturedepend on Temperature

Object

YouHeat LampCandle FlameBulb FilamentSunrsquos Surface

Temperature

~ 30 C~ 500 C~ 1700 C~ 2700 C~ 5500 C

Color

Infrared (invisible)Dull redDim orangeYellowBrilliant white

The hotter it gets the ldquobluerrdquo the emitted lightThe hotter it gets the more intense the radiation (more energy)

UCSD Physics 12

Spring 2013 15

ldquoldquoBlackbodyrdquo or Planck SpectrumBlackbodyrdquo or Planck Spectrum

UCSD Physics 12

Spring 2013 16

Same thing on logarithmic scaleSame thing on logarithmic scale

Sun peaks in visible band (05 microns) light bulbs at 1 m we at 10 m(note 0degC = 273degK 300degK = 27degC = 81degF)

UCSD Physics 12

Spring 2013 17

Okay but how much energyOkay but how much energy

bull The power given off of a surface in the form of light is The power given off of a surface in the form of light is proportional to the proportional to the fourth powerfourth power of temperature of temperature

F = F = TT44 in Watts per square meter in Watts per square meterndash the constant is numerically 56710-8 WordmK4m2

ndash easy to remember constant 5678

ndash temperature must be in Kelvinbull ordmK = ordmC + 273

bull ordmC = (59)(ordmF ndash32)

bull Example radiation from your bodyExample radiation from your body(567 10-8) (310)4 = 523 Watts per square meter

(if naked in the cold of space donrsquot let this happen to you)

UCSD Physics 12

Spring 2013 18

Radiant Energy continuedRadiant Energy continued

bull Example The sun is 5800Example The sun is 5800ordmK on its surface soordmK on its surface soF = T4 = (56710-8)(5800)4 = 64107 Wm2

Summing over entire surface area of sun gives 391026 W

bull Compare to total capacity of energy production on Compare to total capacity of energy production on earth 33earth 3310101212 W Wndash Single power plant typically 05ndash10 GW (109 W)

bull In earthly situations radiated power out partially In earthly situations radiated power out partially balanced by radiated power in from other sourcesbalanced by radiated power in from other sourcesndash Not 523 Wm2 in 70ordmF room more like 100 Wm2

bull goes like Th4 ndash Tc

4

Q

UCSD Physics 12

Spring 2013 19

And those are the major playershellipAnd those are the major playershellip

bull Wersquove now seen all the major energy players wersquoll Wersquove now seen all the major energy players wersquoll be discussing in this classbe discussing in this classndash work as force times distance

ndash kinetic energy (wind ocean currents)

ndash gravitational potential energy (hydroelectric tidal)

ndash chemical energy (fossil fuels batteries food biomass)

ndash heat energy (power plants space heating)

ndash mass-energy (nuclear sources sunrsquos energy)

ndash radiant energy (solar energy)

UCSD Physics 12

Spring 2013 20

AssignmentsAssignments

bull Homework 1 due April 12 in classHomework 1 due April 12 in classndash Chapter 1 problems plus online additions

bull see assignments link on web page for details

ndash donrsquot forget to show your workreasoning on the multiple choice

bull the answers alone do not suffice

bull Quiz 1 due Friday April 12 by midnightQuiz 1 due Friday April 12 by midnightndash TED will be up and quizzes available by Thursday

ndash 3 attempts permitted

ndash all numericalquantitative this week

UCSD Physics 12

Spring 2013 7

Nutrition LabelsNutrition Labels

bull Nutrition labels tell you about the Nutrition labels tell you about the energy content of foodenergy content of food

bull Note that capital C means kcalNote that capital C means kcalbull Conversions Conversions Fat 9 kcalgFat 9 kcalg

Carbs 4 kcalgCarbs 4 kcalgProtein 4 kcalgProtein 4 kcalg

bull This product has 72 kcal from fat 48 This product has 72 kcal from fat 48 kcal from carbohydrates and 32 kcal kcal from carbohydrates and 32 kcal from proteinfrom proteinndash sum is 152 kilocalories compare to label

bull 152 kcal = 636 kJ enough to climb 152 kcal = 636 kJ enough to climb about 1000 meters (64 kg person)about 1000 meters (64 kg person)

Q

UCSD Physics 12

Spring 2013 8

Our Human Energy BudgetOur Human Energy Budget

bull A 2000 kcal per day diet A 2000 kcal per day diet means 2000means 20004184 J = 4184 J = 8368000 J per day8368000 J per day

bull 837 MJ837 MJ in (24 hrday) in (24 hrday) (60 minhr)(60 minhr)(60 (60 secmin) = 86400 sec secmin) = 86400 sec corresponds to corresponds to 97 Watts 97 Watts of powerof power

bull Even a couch-potato at Even a couch-potato at 1500 kcalday burns 1500 kcalday burns 75 W75 W

bull More active lifestyles More active lifestyles require greater caloric require greater caloric intake (more energy)intake (more energy)

UCSD Physics 12

Spring 2013 9

Mass-energyMass-energy

bull Einsteinrsquos famous relationEinsteinrsquos famous relationE = mcE = mc22

relates mass to energyrelates mass to energybull In effect they In effect they areare the same thing the same thing

ndash one can be transformed into the otherndash physicists speak generally of mass-energy

bull Seldom experienced in daily life directlySeldom experienced in daily life directlyndash Happens at large scale in the center of the sun and in

nuclear bombs and reactorsndash Actually does happen at barely detectable level in all

energy transactions but the effect is tiny

UCSD Physics 12

Spring 2013 10

E = mcE = mc22 Examples Examples

bull The energy equivalent of one gram of material The energy equivalent of one gram of material ((any compositionany composition) is (0001 kg)) is (0001 kg)(30(30101088 ms) ms)22 = 90= 9010101313 J = 90000000000000 J = 90 TJ J = 90000000000000 J = 90 TJndash Man thatrsquos big

ndash The US energy budget is equivalent to 1000 kgyr

bull If one gram of material undergoes a If one gram of material undergoes a chemical chemical reaction losing about 9000 J of energy how reaction losing about 9000 J of energy how much much massmass does it lose does it lose

9000 J = mc2 so m = 9000c2 = 910391016

= 10-13 kg (would we ever notice)

UCSD Physics 12

Spring 2013 11

Solar Energy is Nuclear Using Solar Energy is Nuclear Using EE = = mcmc22

bull Thermonuclear fusion reactions in the sunrsquos centerThermonuclear fusion reactions in the sunrsquos centerndash Sun is 16 million degrees Celsius in its center

ndash Enough energy to ram protons together (despite mutual repulsion) and make deuterium then helium

ndash Reaction per atom 20 million times more energetic than chemical reactions in general

4 protonsmass = 4029

4He nucleusmass = 40015

2 neutrinos photons (light)

UCSD Physics 12

Spring 2013 12

EE = = mcmc22 in Sun in Sun

bull Helium nucleus is Helium nucleus is lighterlighter than the four protons than the four protonsbull Mass difference is 4029 Mass difference is 4029 40015 = 00276 amu 40015 = 00276 amu

ndash 1 amu (atomic mass unit) is 1660510-27 kg

ndash difference of 45810-29 kg

ndash multiply by c2 to get 41210-12 J

ndash 1 mole (60221023 particles) of protons 251012 J

ndash typical chemical reactions are 100-200 kJmole

ndash nuclear fusion is ~20 million times more potent stuff

Q

UCSD Physics 12

Spring 2013 13

Energy from LightEnergy from Light

bull The tremendous energy from the sun is released as The tremendous energy from the sun is released as light So light carries energylight So light carries energy

bull How muchHow muchbull Best way to get at this is through the process of Best way to get at this is through the process of

ldquoblackbodyrdquo radiation or thermal radiationhellipldquoblackbodyrdquo radiation or thermal radiationhellipbull All objects emit ldquolightrdquoAll objects emit ldquolightrdquo

ndash Though almost all the light we see is reflected light

bull The color and intensity of the emitted radiation The color and intensity of the emitted radiation depend on the objectrsquos temperaturedepend on the objectrsquos temperature

UCSD Physics 12

Spring 2013 14

Emitted Radiationrsquos Color and Intensity Emitted Radiationrsquos Color and Intensity depend on Temperaturedepend on Temperature

Object

YouHeat LampCandle FlameBulb FilamentSunrsquos Surface

Temperature

~ 30 C~ 500 C~ 1700 C~ 2700 C~ 5500 C

Color

Infrared (invisible)Dull redDim orangeYellowBrilliant white

The hotter it gets the ldquobluerrdquo the emitted lightThe hotter it gets the more intense the radiation (more energy)

UCSD Physics 12

Spring 2013 15

ldquoldquoBlackbodyrdquo or Planck SpectrumBlackbodyrdquo or Planck Spectrum

UCSD Physics 12

Spring 2013 16

Same thing on logarithmic scaleSame thing on logarithmic scale

Sun peaks in visible band (05 microns) light bulbs at 1 m we at 10 m(note 0degC = 273degK 300degK = 27degC = 81degF)

UCSD Physics 12

Spring 2013 17

Okay but how much energyOkay but how much energy

bull The power given off of a surface in the form of light is The power given off of a surface in the form of light is proportional to the proportional to the fourth powerfourth power of temperature of temperature

F = F = TT44 in Watts per square meter in Watts per square meterndash the constant is numerically 56710-8 WordmK4m2

ndash easy to remember constant 5678

ndash temperature must be in Kelvinbull ordmK = ordmC + 273

bull ordmC = (59)(ordmF ndash32)

bull Example radiation from your bodyExample radiation from your body(567 10-8) (310)4 = 523 Watts per square meter

(if naked in the cold of space donrsquot let this happen to you)

UCSD Physics 12

Spring 2013 18

Radiant Energy continuedRadiant Energy continued

bull Example The sun is 5800Example The sun is 5800ordmK on its surface soordmK on its surface soF = T4 = (56710-8)(5800)4 = 64107 Wm2

Summing over entire surface area of sun gives 391026 W

bull Compare to total capacity of energy production on Compare to total capacity of energy production on earth 33earth 3310101212 W Wndash Single power plant typically 05ndash10 GW (109 W)

bull In earthly situations radiated power out partially In earthly situations radiated power out partially balanced by radiated power in from other sourcesbalanced by radiated power in from other sourcesndash Not 523 Wm2 in 70ordmF room more like 100 Wm2

bull goes like Th4 ndash Tc

4

Q

UCSD Physics 12

Spring 2013 19

And those are the major playershellipAnd those are the major playershellip

bull Wersquove now seen all the major energy players wersquoll Wersquove now seen all the major energy players wersquoll be discussing in this classbe discussing in this classndash work as force times distance

ndash kinetic energy (wind ocean currents)

ndash gravitational potential energy (hydroelectric tidal)

ndash chemical energy (fossil fuels batteries food biomass)

ndash heat energy (power plants space heating)

ndash mass-energy (nuclear sources sunrsquos energy)

ndash radiant energy (solar energy)

UCSD Physics 12

Spring 2013 20

AssignmentsAssignments

bull Homework 1 due April 12 in classHomework 1 due April 12 in classndash Chapter 1 problems plus online additions

bull see assignments link on web page for details

ndash donrsquot forget to show your workreasoning on the multiple choice

bull the answers alone do not suffice

bull Quiz 1 due Friday April 12 by midnightQuiz 1 due Friday April 12 by midnightndash TED will be up and quizzes available by Thursday

ndash 3 attempts permitted

ndash all numericalquantitative this week

UCSD Physics 12

Spring 2013 8

Our Human Energy BudgetOur Human Energy Budget

bull A 2000 kcal per day diet A 2000 kcal per day diet means 2000means 20004184 J = 4184 J = 8368000 J per day8368000 J per day

bull 837 MJ837 MJ in (24 hrday) in (24 hrday) (60 minhr)(60 minhr)(60 (60 secmin) = 86400 sec secmin) = 86400 sec corresponds to corresponds to 97 Watts 97 Watts of powerof power

bull Even a couch-potato at Even a couch-potato at 1500 kcalday burns 1500 kcalday burns 75 W75 W

bull More active lifestyles More active lifestyles require greater caloric require greater caloric intake (more energy)intake (more energy)

UCSD Physics 12

Spring 2013 9

Mass-energyMass-energy

bull Einsteinrsquos famous relationEinsteinrsquos famous relationE = mcE = mc22

relates mass to energyrelates mass to energybull In effect they In effect they areare the same thing the same thing

ndash one can be transformed into the otherndash physicists speak generally of mass-energy

bull Seldom experienced in daily life directlySeldom experienced in daily life directlyndash Happens at large scale in the center of the sun and in

nuclear bombs and reactorsndash Actually does happen at barely detectable level in all

energy transactions but the effect is tiny

UCSD Physics 12

Spring 2013 10

E = mcE = mc22 Examples Examples

bull The energy equivalent of one gram of material The energy equivalent of one gram of material ((any compositionany composition) is (0001 kg)) is (0001 kg)(30(30101088 ms) ms)22 = 90= 9010101313 J = 90000000000000 J = 90 TJ J = 90000000000000 J = 90 TJndash Man thatrsquos big

ndash The US energy budget is equivalent to 1000 kgyr

bull If one gram of material undergoes a If one gram of material undergoes a chemical chemical reaction losing about 9000 J of energy how reaction losing about 9000 J of energy how much much massmass does it lose does it lose

9000 J = mc2 so m = 9000c2 = 910391016

= 10-13 kg (would we ever notice)

UCSD Physics 12

Spring 2013 11

Solar Energy is Nuclear Using Solar Energy is Nuclear Using EE = = mcmc22

bull Thermonuclear fusion reactions in the sunrsquos centerThermonuclear fusion reactions in the sunrsquos centerndash Sun is 16 million degrees Celsius in its center

ndash Enough energy to ram protons together (despite mutual repulsion) and make deuterium then helium

ndash Reaction per atom 20 million times more energetic than chemical reactions in general

4 protonsmass = 4029

4He nucleusmass = 40015

2 neutrinos photons (light)

UCSD Physics 12

Spring 2013 12

EE = = mcmc22 in Sun in Sun

bull Helium nucleus is Helium nucleus is lighterlighter than the four protons than the four protonsbull Mass difference is 4029 Mass difference is 4029 40015 = 00276 amu 40015 = 00276 amu

ndash 1 amu (atomic mass unit) is 1660510-27 kg

ndash difference of 45810-29 kg

ndash multiply by c2 to get 41210-12 J

ndash 1 mole (60221023 particles) of protons 251012 J

ndash typical chemical reactions are 100-200 kJmole

ndash nuclear fusion is ~20 million times more potent stuff

Q

UCSD Physics 12

Spring 2013 13

Energy from LightEnergy from Light

bull The tremendous energy from the sun is released as The tremendous energy from the sun is released as light So light carries energylight So light carries energy

bull How muchHow muchbull Best way to get at this is through the process of Best way to get at this is through the process of

ldquoblackbodyrdquo radiation or thermal radiationhellipldquoblackbodyrdquo radiation or thermal radiationhellipbull All objects emit ldquolightrdquoAll objects emit ldquolightrdquo

ndash Though almost all the light we see is reflected light

bull The color and intensity of the emitted radiation The color and intensity of the emitted radiation depend on the objectrsquos temperaturedepend on the objectrsquos temperature

UCSD Physics 12

Spring 2013 14

Emitted Radiationrsquos Color and Intensity Emitted Radiationrsquos Color and Intensity depend on Temperaturedepend on Temperature

Object

YouHeat LampCandle FlameBulb FilamentSunrsquos Surface

Temperature

~ 30 C~ 500 C~ 1700 C~ 2700 C~ 5500 C

Color

Infrared (invisible)Dull redDim orangeYellowBrilliant white

The hotter it gets the ldquobluerrdquo the emitted lightThe hotter it gets the more intense the radiation (more energy)

UCSD Physics 12

Spring 2013 15

ldquoldquoBlackbodyrdquo or Planck SpectrumBlackbodyrdquo or Planck Spectrum

UCSD Physics 12

Spring 2013 16

Same thing on logarithmic scaleSame thing on logarithmic scale

Sun peaks in visible band (05 microns) light bulbs at 1 m we at 10 m(note 0degC = 273degK 300degK = 27degC = 81degF)

UCSD Physics 12

Spring 2013 17

Okay but how much energyOkay but how much energy

bull The power given off of a surface in the form of light is The power given off of a surface in the form of light is proportional to the proportional to the fourth powerfourth power of temperature of temperature

F = F = TT44 in Watts per square meter in Watts per square meterndash the constant is numerically 56710-8 WordmK4m2

ndash easy to remember constant 5678

ndash temperature must be in Kelvinbull ordmK = ordmC + 273

bull ordmC = (59)(ordmF ndash32)

bull Example radiation from your bodyExample radiation from your body(567 10-8) (310)4 = 523 Watts per square meter

(if naked in the cold of space donrsquot let this happen to you)

UCSD Physics 12

Spring 2013 18

Radiant Energy continuedRadiant Energy continued

bull Example The sun is 5800Example The sun is 5800ordmK on its surface soordmK on its surface soF = T4 = (56710-8)(5800)4 = 64107 Wm2

Summing over entire surface area of sun gives 391026 W

bull Compare to total capacity of energy production on Compare to total capacity of energy production on earth 33earth 3310101212 W Wndash Single power plant typically 05ndash10 GW (109 W)

bull In earthly situations radiated power out partially In earthly situations radiated power out partially balanced by radiated power in from other sourcesbalanced by radiated power in from other sourcesndash Not 523 Wm2 in 70ordmF room more like 100 Wm2

bull goes like Th4 ndash Tc

4

Q

UCSD Physics 12

Spring 2013 19

And those are the major playershellipAnd those are the major playershellip

bull Wersquove now seen all the major energy players wersquoll Wersquove now seen all the major energy players wersquoll be discussing in this classbe discussing in this classndash work as force times distance

ndash kinetic energy (wind ocean currents)

ndash gravitational potential energy (hydroelectric tidal)

ndash chemical energy (fossil fuels batteries food biomass)

ndash heat energy (power plants space heating)

ndash mass-energy (nuclear sources sunrsquos energy)

ndash radiant energy (solar energy)

UCSD Physics 12

Spring 2013 20

AssignmentsAssignments

bull Homework 1 due April 12 in classHomework 1 due April 12 in classndash Chapter 1 problems plus online additions

bull see assignments link on web page for details

ndash donrsquot forget to show your workreasoning on the multiple choice

bull the answers alone do not suffice

bull Quiz 1 due Friday April 12 by midnightQuiz 1 due Friday April 12 by midnightndash TED will be up and quizzes available by Thursday

ndash 3 attempts permitted

ndash all numericalquantitative this week

UCSD Physics 12

Spring 2013 9

Mass-energyMass-energy

bull Einsteinrsquos famous relationEinsteinrsquos famous relationE = mcE = mc22

relates mass to energyrelates mass to energybull In effect they In effect they areare the same thing the same thing

ndash one can be transformed into the otherndash physicists speak generally of mass-energy

bull Seldom experienced in daily life directlySeldom experienced in daily life directlyndash Happens at large scale in the center of the sun and in

nuclear bombs and reactorsndash Actually does happen at barely detectable level in all

energy transactions but the effect is tiny

UCSD Physics 12

Spring 2013 10

E = mcE = mc22 Examples Examples

bull The energy equivalent of one gram of material The energy equivalent of one gram of material ((any compositionany composition) is (0001 kg)) is (0001 kg)(30(30101088 ms) ms)22 = 90= 9010101313 J = 90000000000000 J = 90 TJ J = 90000000000000 J = 90 TJndash Man thatrsquos big

ndash The US energy budget is equivalent to 1000 kgyr

bull If one gram of material undergoes a If one gram of material undergoes a chemical chemical reaction losing about 9000 J of energy how reaction losing about 9000 J of energy how much much massmass does it lose does it lose

9000 J = mc2 so m = 9000c2 = 910391016

= 10-13 kg (would we ever notice)

UCSD Physics 12

Spring 2013 11

Solar Energy is Nuclear Using Solar Energy is Nuclear Using EE = = mcmc22

bull Thermonuclear fusion reactions in the sunrsquos centerThermonuclear fusion reactions in the sunrsquos centerndash Sun is 16 million degrees Celsius in its center

ndash Enough energy to ram protons together (despite mutual repulsion) and make deuterium then helium

ndash Reaction per atom 20 million times more energetic than chemical reactions in general

4 protonsmass = 4029

4He nucleusmass = 40015

2 neutrinos photons (light)

UCSD Physics 12

Spring 2013 12

EE = = mcmc22 in Sun in Sun

bull Helium nucleus is Helium nucleus is lighterlighter than the four protons than the four protonsbull Mass difference is 4029 Mass difference is 4029 40015 = 00276 amu 40015 = 00276 amu

ndash 1 amu (atomic mass unit) is 1660510-27 kg

ndash difference of 45810-29 kg

ndash multiply by c2 to get 41210-12 J

ndash 1 mole (60221023 particles) of protons 251012 J

ndash typical chemical reactions are 100-200 kJmole

ndash nuclear fusion is ~20 million times more potent stuff

Q

UCSD Physics 12

Spring 2013 13

Energy from LightEnergy from Light

bull The tremendous energy from the sun is released as The tremendous energy from the sun is released as light So light carries energylight So light carries energy

bull How muchHow muchbull Best way to get at this is through the process of Best way to get at this is through the process of

ldquoblackbodyrdquo radiation or thermal radiationhellipldquoblackbodyrdquo radiation or thermal radiationhellipbull All objects emit ldquolightrdquoAll objects emit ldquolightrdquo

ndash Though almost all the light we see is reflected light

bull The color and intensity of the emitted radiation The color and intensity of the emitted radiation depend on the objectrsquos temperaturedepend on the objectrsquos temperature

UCSD Physics 12

Spring 2013 14

Emitted Radiationrsquos Color and Intensity Emitted Radiationrsquos Color and Intensity depend on Temperaturedepend on Temperature

Object

YouHeat LampCandle FlameBulb FilamentSunrsquos Surface

Temperature

~ 30 C~ 500 C~ 1700 C~ 2700 C~ 5500 C

Color

Infrared (invisible)Dull redDim orangeYellowBrilliant white

The hotter it gets the ldquobluerrdquo the emitted lightThe hotter it gets the more intense the radiation (more energy)

UCSD Physics 12

Spring 2013 15

ldquoldquoBlackbodyrdquo or Planck SpectrumBlackbodyrdquo or Planck Spectrum

UCSD Physics 12

Spring 2013 16

Same thing on logarithmic scaleSame thing on logarithmic scale

Sun peaks in visible band (05 microns) light bulbs at 1 m we at 10 m(note 0degC = 273degK 300degK = 27degC = 81degF)

UCSD Physics 12

Spring 2013 17

Okay but how much energyOkay but how much energy

bull The power given off of a surface in the form of light is The power given off of a surface in the form of light is proportional to the proportional to the fourth powerfourth power of temperature of temperature

F = F = TT44 in Watts per square meter in Watts per square meterndash the constant is numerically 56710-8 WordmK4m2

ndash easy to remember constant 5678

ndash temperature must be in Kelvinbull ordmK = ordmC + 273

bull ordmC = (59)(ordmF ndash32)

bull Example radiation from your bodyExample radiation from your body(567 10-8) (310)4 = 523 Watts per square meter

(if naked in the cold of space donrsquot let this happen to you)

UCSD Physics 12

Spring 2013 18

Radiant Energy continuedRadiant Energy continued

bull Example The sun is 5800Example The sun is 5800ordmK on its surface soordmK on its surface soF = T4 = (56710-8)(5800)4 = 64107 Wm2

Summing over entire surface area of sun gives 391026 W

bull Compare to total capacity of energy production on Compare to total capacity of energy production on earth 33earth 3310101212 W Wndash Single power plant typically 05ndash10 GW (109 W)

bull In earthly situations radiated power out partially In earthly situations radiated power out partially balanced by radiated power in from other sourcesbalanced by radiated power in from other sourcesndash Not 523 Wm2 in 70ordmF room more like 100 Wm2

bull goes like Th4 ndash Tc

4

Q

UCSD Physics 12

Spring 2013 19

And those are the major playershellipAnd those are the major playershellip

bull Wersquove now seen all the major energy players wersquoll Wersquove now seen all the major energy players wersquoll be discussing in this classbe discussing in this classndash work as force times distance

ndash kinetic energy (wind ocean currents)

ndash gravitational potential energy (hydroelectric tidal)

ndash chemical energy (fossil fuels batteries food biomass)

ndash heat energy (power plants space heating)

ndash mass-energy (nuclear sources sunrsquos energy)

ndash radiant energy (solar energy)

UCSD Physics 12

Spring 2013 20

AssignmentsAssignments

bull Homework 1 due April 12 in classHomework 1 due April 12 in classndash Chapter 1 problems plus online additions

bull see assignments link on web page for details

ndash donrsquot forget to show your workreasoning on the multiple choice

bull the answers alone do not suffice

bull Quiz 1 due Friday April 12 by midnightQuiz 1 due Friday April 12 by midnightndash TED will be up and quizzes available by Thursday

ndash 3 attempts permitted

ndash all numericalquantitative this week

UCSD Physics 12

Spring 2013 10

E = mcE = mc22 Examples Examples

bull The energy equivalent of one gram of material The energy equivalent of one gram of material ((any compositionany composition) is (0001 kg)) is (0001 kg)(30(30101088 ms) ms)22 = 90= 9010101313 J = 90000000000000 J = 90 TJ J = 90000000000000 J = 90 TJndash Man thatrsquos big

ndash The US energy budget is equivalent to 1000 kgyr

bull If one gram of material undergoes a If one gram of material undergoes a chemical chemical reaction losing about 9000 J of energy how reaction losing about 9000 J of energy how much much massmass does it lose does it lose

9000 J = mc2 so m = 9000c2 = 910391016

= 10-13 kg (would we ever notice)

UCSD Physics 12

Spring 2013 11

Solar Energy is Nuclear Using Solar Energy is Nuclear Using EE = = mcmc22

bull Thermonuclear fusion reactions in the sunrsquos centerThermonuclear fusion reactions in the sunrsquos centerndash Sun is 16 million degrees Celsius in its center

ndash Enough energy to ram protons together (despite mutual repulsion) and make deuterium then helium

ndash Reaction per atom 20 million times more energetic than chemical reactions in general

4 protonsmass = 4029

4He nucleusmass = 40015

2 neutrinos photons (light)

UCSD Physics 12

Spring 2013 12

EE = = mcmc22 in Sun in Sun

bull Helium nucleus is Helium nucleus is lighterlighter than the four protons than the four protonsbull Mass difference is 4029 Mass difference is 4029 40015 = 00276 amu 40015 = 00276 amu

ndash 1 amu (atomic mass unit) is 1660510-27 kg

ndash difference of 45810-29 kg

ndash multiply by c2 to get 41210-12 J

ndash 1 mole (60221023 particles) of protons 251012 J

ndash typical chemical reactions are 100-200 kJmole

ndash nuclear fusion is ~20 million times more potent stuff

Q

UCSD Physics 12

Spring 2013 13

Energy from LightEnergy from Light

bull The tremendous energy from the sun is released as The tremendous energy from the sun is released as light So light carries energylight So light carries energy

bull How muchHow muchbull Best way to get at this is through the process of Best way to get at this is through the process of

ldquoblackbodyrdquo radiation or thermal radiationhellipldquoblackbodyrdquo radiation or thermal radiationhellipbull All objects emit ldquolightrdquoAll objects emit ldquolightrdquo

ndash Though almost all the light we see is reflected light

bull The color and intensity of the emitted radiation The color and intensity of the emitted radiation depend on the objectrsquos temperaturedepend on the objectrsquos temperature

UCSD Physics 12

Spring 2013 14

Emitted Radiationrsquos Color and Intensity Emitted Radiationrsquos Color and Intensity depend on Temperaturedepend on Temperature

Object

YouHeat LampCandle FlameBulb FilamentSunrsquos Surface

Temperature

~ 30 C~ 500 C~ 1700 C~ 2700 C~ 5500 C

Color

Infrared (invisible)Dull redDim orangeYellowBrilliant white

The hotter it gets the ldquobluerrdquo the emitted lightThe hotter it gets the more intense the radiation (more energy)

UCSD Physics 12

Spring 2013 15

ldquoldquoBlackbodyrdquo or Planck SpectrumBlackbodyrdquo or Planck Spectrum

UCSD Physics 12

Spring 2013 16

Same thing on logarithmic scaleSame thing on logarithmic scale

Sun peaks in visible band (05 microns) light bulbs at 1 m we at 10 m(note 0degC = 273degK 300degK = 27degC = 81degF)

UCSD Physics 12

Spring 2013 17

Okay but how much energyOkay but how much energy

bull The power given off of a surface in the form of light is The power given off of a surface in the form of light is proportional to the proportional to the fourth powerfourth power of temperature of temperature

F = F = TT44 in Watts per square meter in Watts per square meterndash the constant is numerically 56710-8 WordmK4m2

ndash easy to remember constant 5678

ndash temperature must be in Kelvinbull ordmK = ordmC + 273

bull ordmC = (59)(ordmF ndash32)

bull Example radiation from your bodyExample radiation from your body(567 10-8) (310)4 = 523 Watts per square meter

(if naked in the cold of space donrsquot let this happen to you)

UCSD Physics 12

Spring 2013 18

Radiant Energy continuedRadiant Energy continued

bull Example The sun is 5800Example The sun is 5800ordmK on its surface soordmK on its surface soF = T4 = (56710-8)(5800)4 = 64107 Wm2

Summing over entire surface area of sun gives 391026 W

bull Compare to total capacity of energy production on Compare to total capacity of energy production on earth 33earth 3310101212 W Wndash Single power plant typically 05ndash10 GW (109 W)

bull In earthly situations radiated power out partially In earthly situations radiated power out partially balanced by radiated power in from other sourcesbalanced by radiated power in from other sourcesndash Not 523 Wm2 in 70ordmF room more like 100 Wm2

bull goes like Th4 ndash Tc

4

Q

UCSD Physics 12

Spring 2013 19

And those are the major playershellipAnd those are the major playershellip

bull Wersquove now seen all the major energy players wersquoll Wersquove now seen all the major energy players wersquoll be discussing in this classbe discussing in this classndash work as force times distance

ndash kinetic energy (wind ocean currents)

ndash gravitational potential energy (hydroelectric tidal)

ndash chemical energy (fossil fuels batteries food biomass)

ndash heat energy (power plants space heating)

ndash mass-energy (nuclear sources sunrsquos energy)

ndash radiant energy (solar energy)

UCSD Physics 12

Spring 2013 20

AssignmentsAssignments

bull Homework 1 due April 12 in classHomework 1 due April 12 in classndash Chapter 1 problems plus online additions

bull see assignments link on web page for details

ndash donrsquot forget to show your workreasoning on the multiple choice

bull the answers alone do not suffice

bull Quiz 1 due Friday April 12 by midnightQuiz 1 due Friday April 12 by midnightndash TED will be up and quizzes available by Thursday

ndash 3 attempts permitted

ndash all numericalquantitative this week

UCSD Physics 12

Spring 2013 11

Solar Energy is Nuclear Using Solar Energy is Nuclear Using EE = = mcmc22

bull Thermonuclear fusion reactions in the sunrsquos centerThermonuclear fusion reactions in the sunrsquos centerndash Sun is 16 million degrees Celsius in its center

ndash Enough energy to ram protons together (despite mutual repulsion) and make deuterium then helium

ndash Reaction per atom 20 million times more energetic than chemical reactions in general

4 protonsmass = 4029

4He nucleusmass = 40015

2 neutrinos photons (light)

UCSD Physics 12

Spring 2013 12

EE = = mcmc22 in Sun in Sun

bull Helium nucleus is Helium nucleus is lighterlighter than the four protons than the four protonsbull Mass difference is 4029 Mass difference is 4029 40015 = 00276 amu 40015 = 00276 amu

ndash 1 amu (atomic mass unit) is 1660510-27 kg

ndash difference of 45810-29 kg

ndash multiply by c2 to get 41210-12 J

ndash 1 mole (60221023 particles) of protons 251012 J

ndash typical chemical reactions are 100-200 kJmole

ndash nuclear fusion is ~20 million times more potent stuff

Q

UCSD Physics 12

Spring 2013 13

Energy from LightEnergy from Light

bull The tremendous energy from the sun is released as The tremendous energy from the sun is released as light So light carries energylight So light carries energy

bull How muchHow muchbull Best way to get at this is through the process of Best way to get at this is through the process of

ldquoblackbodyrdquo radiation or thermal radiationhellipldquoblackbodyrdquo radiation or thermal radiationhellipbull All objects emit ldquolightrdquoAll objects emit ldquolightrdquo

ndash Though almost all the light we see is reflected light

bull The color and intensity of the emitted radiation The color and intensity of the emitted radiation depend on the objectrsquos temperaturedepend on the objectrsquos temperature

UCSD Physics 12

Spring 2013 14

Emitted Radiationrsquos Color and Intensity Emitted Radiationrsquos Color and Intensity depend on Temperaturedepend on Temperature

Object

YouHeat LampCandle FlameBulb FilamentSunrsquos Surface

Temperature

~ 30 C~ 500 C~ 1700 C~ 2700 C~ 5500 C

Color

Infrared (invisible)Dull redDim orangeYellowBrilliant white

The hotter it gets the ldquobluerrdquo the emitted lightThe hotter it gets the more intense the radiation (more energy)

UCSD Physics 12

Spring 2013 15

ldquoldquoBlackbodyrdquo or Planck SpectrumBlackbodyrdquo or Planck Spectrum

UCSD Physics 12

Spring 2013 16

Same thing on logarithmic scaleSame thing on logarithmic scale

Sun peaks in visible band (05 microns) light bulbs at 1 m we at 10 m(note 0degC = 273degK 300degK = 27degC = 81degF)

UCSD Physics 12

Spring 2013 17

Okay but how much energyOkay but how much energy

bull The power given off of a surface in the form of light is The power given off of a surface in the form of light is proportional to the proportional to the fourth powerfourth power of temperature of temperature

F = F = TT44 in Watts per square meter in Watts per square meterndash the constant is numerically 56710-8 WordmK4m2

ndash easy to remember constant 5678

ndash temperature must be in Kelvinbull ordmK = ordmC + 273

bull ordmC = (59)(ordmF ndash32)

bull Example radiation from your bodyExample radiation from your body(567 10-8) (310)4 = 523 Watts per square meter

(if naked in the cold of space donrsquot let this happen to you)

UCSD Physics 12

Spring 2013 18

Radiant Energy continuedRadiant Energy continued

bull Example The sun is 5800Example The sun is 5800ordmK on its surface soordmK on its surface soF = T4 = (56710-8)(5800)4 = 64107 Wm2

Summing over entire surface area of sun gives 391026 W

bull Compare to total capacity of energy production on Compare to total capacity of energy production on earth 33earth 3310101212 W Wndash Single power plant typically 05ndash10 GW (109 W)

bull In earthly situations radiated power out partially In earthly situations radiated power out partially balanced by radiated power in from other sourcesbalanced by radiated power in from other sourcesndash Not 523 Wm2 in 70ordmF room more like 100 Wm2

bull goes like Th4 ndash Tc

4

Q

UCSD Physics 12

Spring 2013 19

And those are the major playershellipAnd those are the major playershellip

bull Wersquove now seen all the major energy players wersquoll Wersquove now seen all the major energy players wersquoll be discussing in this classbe discussing in this classndash work as force times distance

ndash kinetic energy (wind ocean currents)

ndash gravitational potential energy (hydroelectric tidal)

ndash chemical energy (fossil fuels batteries food biomass)

ndash heat energy (power plants space heating)

ndash mass-energy (nuclear sources sunrsquos energy)

ndash radiant energy (solar energy)

UCSD Physics 12

Spring 2013 20

AssignmentsAssignments

bull Homework 1 due April 12 in classHomework 1 due April 12 in classndash Chapter 1 problems plus online additions

bull see assignments link on web page for details

ndash donrsquot forget to show your workreasoning on the multiple choice

bull the answers alone do not suffice

bull Quiz 1 due Friday April 12 by midnightQuiz 1 due Friday April 12 by midnightndash TED will be up and quizzes available by Thursday

ndash 3 attempts permitted

ndash all numericalquantitative this week

UCSD Physics 12

Spring 2013 12

EE = = mcmc22 in Sun in Sun

bull Helium nucleus is Helium nucleus is lighterlighter than the four protons than the four protonsbull Mass difference is 4029 Mass difference is 4029 40015 = 00276 amu 40015 = 00276 amu

ndash 1 amu (atomic mass unit) is 1660510-27 kg

ndash difference of 45810-29 kg

ndash multiply by c2 to get 41210-12 J

ndash 1 mole (60221023 particles) of protons 251012 J

ndash typical chemical reactions are 100-200 kJmole

ndash nuclear fusion is ~20 million times more potent stuff

Q

UCSD Physics 12

Spring 2013 13

Energy from LightEnergy from Light

bull The tremendous energy from the sun is released as The tremendous energy from the sun is released as light So light carries energylight So light carries energy

bull How muchHow muchbull Best way to get at this is through the process of Best way to get at this is through the process of

ldquoblackbodyrdquo radiation or thermal radiationhellipldquoblackbodyrdquo radiation or thermal radiationhellipbull All objects emit ldquolightrdquoAll objects emit ldquolightrdquo

ndash Though almost all the light we see is reflected light

bull The color and intensity of the emitted radiation The color and intensity of the emitted radiation depend on the objectrsquos temperaturedepend on the objectrsquos temperature

UCSD Physics 12

Spring 2013 14

Emitted Radiationrsquos Color and Intensity Emitted Radiationrsquos Color and Intensity depend on Temperaturedepend on Temperature

Object

YouHeat LampCandle FlameBulb FilamentSunrsquos Surface

Temperature

~ 30 C~ 500 C~ 1700 C~ 2700 C~ 5500 C

Color

Infrared (invisible)Dull redDim orangeYellowBrilliant white

The hotter it gets the ldquobluerrdquo the emitted lightThe hotter it gets the more intense the radiation (more energy)

UCSD Physics 12

Spring 2013 15

ldquoldquoBlackbodyrdquo or Planck SpectrumBlackbodyrdquo or Planck Spectrum

UCSD Physics 12

Spring 2013 16

Same thing on logarithmic scaleSame thing on logarithmic scale

Sun peaks in visible band (05 microns) light bulbs at 1 m we at 10 m(note 0degC = 273degK 300degK = 27degC = 81degF)

UCSD Physics 12

Spring 2013 17

Okay but how much energyOkay but how much energy

bull The power given off of a surface in the form of light is The power given off of a surface in the form of light is proportional to the proportional to the fourth powerfourth power of temperature of temperature

F = F = TT44 in Watts per square meter in Watts per square meterndash the constant is numerically 56710-8 WordmK4m2

ndash easy to remember constant 5678

ndash temperature must be in Kelvinbull ordmK = ordmC + 273

bull ordmC = (59)(ordmF ndash32)

bull Example radiation from your bodyExample radiation from your body(567 10-8) (310)4 = 523 Watts per square meter

(if naked in the cold of space donrsquot let this happen to you)

UCSD Physics 12

Spring 2013 18

Radiant Energy continuedRadiant Energy continued

bull Example The sun is 5800Example The sun is 5800ordmK on its surface soordmK on its surface soF = T4 = (56710-8)(5800)4 = 64107 Wm2

Summing over entire surface area of sun gives 391026 W

bull Compare to total capacity of energy production on Compare to total capacity of energy production on earth 33earth 3310101212 W Wndash Single power plant typically 05ndash10 GW (109 W)

bull In earthly situations radiated power out partially In earthly situations radiated power out partially balanced by radiated power in from other sourcesbalanced by radiated power in from other sourcesndash Not 523 Wm2 in 70ordmF room more like 100 Wm2

bull goes like Th4 ndash Tc

4

Q

UCSD Physics 12

Spring 2013 19

And those are the major playershellipAnd those are the major playershellip

bull Wersquove now seen all the major energy players wersquoll Wersquove now seen all the major energy players wersquoll be discussing in this classbe discussing in this classndash work as force times distance

ndash kinetic energy (wind ocean currents)

ndash gravitational potential energy (hydroelectric tidal)

ndash chemical energy (fossil fuels batteries food biomass)

ndash heat energy (power plants space heating)

ndash mass-energy (nuclear sources sunrsquos energy)

ndash radiant energy (solar energy)

UCSD Physics 12

Spring 2013 20

AssignmentsAssignments

bull Homework 1 due April 12 in classHomework 1 due April 12 in classndash Chapter 1 problems plus online additions

bull see assignments link on web page for details

ndash donrsquot forget to show your workreasoning on the multiple choice

bull the answers alone do not suffice

bull Quiz 1 due Friday April 12 by midnightQuiz 1 due Friday April 12 by midnightndash TED will be up and quizzes available by Thursday

ndash 3 attempts permitted

ndash all numericalquantitative this week

UCSD Physics 12

Spring 2013 13

Energy from LightEnergy from Light

bull The tremendous energy from the sun is released as The tremendous energy from the sun is released as light So light carries energylight So light carries energy

bull How muchHow muchbull Best way to get at this is through the process of Best way to get at this is through the process of

ldquoblackbodyrdquo radiation or thermal radiationhellipldquoblackbodyrdquo radiation or thermal radiationhellipbull All objects emit ldquolightrdquoAll objects emit ldquolightrdquo

ndash Though almost all the light we see is reflected light

bull The color and intensity of the emitted radiation The color and intensity of the emitted radiation depend on the objectrsquos temperaturedepend on the objectrsquos temperature

UCSD Physics 12

Spring 2013 14

Emitted Radiationrsquos Color and Intensity Emitted Radiationrsquos Color and Intensity depend on Temperaturedepend on Temperature

Object

YouHeat LampCandle FlameBulb FilamentSunrsquos Surface

Temperature

~ 30 C~ 500 C~ 1700 C~ 2700 C~ 5500 C

Color

Infrared (invisible)Dull redDim orangeYellowBrilliant white

The hotter it gets the ldquobluerrdquo the emitted lightThe hotter it gets the more intense the radiation (more energy)

UCSD Physics 12

Spring 2013 15

ldquoldquoBlackbodyrdquo or Planck SpectrumBlackbodyrdquo or Planck Spectrum

UCSD Physics 12

Spring 2013 16

Same thing on logarithmic scaleSame thing on logarithmic scale

Sun peaks in visible band (05 microns) light bulbs at 1 m we at 10 m(note 0degC = 273degK 300degK = 27degC = 81degF)

UCSD Physics 12

Spring 2013 17

Okay but how much energyOkay but how much energy

bull The power given off of a surface in the form of light is The power given off of a surface in the form of light is proportional to the proportional to the fourth powerfourth power of temperature of temperature

F = F = TT44 in Watts per square meter in Watts per square meterndash the constant is numerically 56710-8 WordmK4m2

ndash easy to remember constant 5678

ndash temperature must be in Kelvinbull ordmK = ordmC + 273

bull ordmC = (59)(ordmF ndash32)

bull Example radiation from your bodyExample radiation from your body(567 10-8) (310)4 = 523 Watts per square meter

(if naked in the cold of space donrsquot let this happen to you)

UCSD Physics 12

Spring 2013 18

Radiant Energy continuedRadiant Energy continued

bull Example The sun is 5800Example The sun is 5800ordmK on its surface soordmK on its surface soF = T4 = (56710-8)(5800)4 = 64107 Wm2

Summing over entire surface area of sun gives 391026 W

bull Compare to total capacity of energy production on Compare to total capacity of energy production on earth 33earth 3310101212 W Wndash Single power plant typically 05ndash10 GW (109 W)

bull In earthly situations radiated power out partially In earthly situations radiated power out partially balanced by radiated power in from other sourcesbalanced by radiated power in from other sourcesndash Not 523 Wm2 in 70ordmF room more like 100 Wm2

bull goes like Th4 ndash Tc

4

Q

UCSD Physics 12

Spring 2013 19

And those are the major playershellipAnd those are the major playershellip

bull Wersquove now seen all the major energy players wersquoll Wersquove now seen all the major energy players wersquoll be discussing in this classbe discussing in this classndash work as force times distance

ndash kinetic energy (wind ocean currents)

ndash gravitational potential energy (hydroelectric tidal)

ndash chemical energy (fossil fuels batteries food biomass)

ndash heat energy (power plants space heating)

ndash mass-energy (nuclear sources sunrsquos energy)

ndash radiant energy (solar energy)

UCSD Physics 12

Spring 2013 20

AssignmentsAssignments

bull Homework 1 due April 12 in classHomework 1 due April 12 in classndash Chapter 1 problems plus online additions

bull see assignments link on web page for details

ndash donrsquot forget to show your workreasoning on the multiple choice

bull the answers alone do not suffice

bull Quiz 1 due Friday April 12 by midnightQuiz 1 due Friday April 12 by midnightndash TED will be up and quizzes available by Thursday

ndash 3 attempts permitted

ndash all numericalquantitative this week

UCSD Physics 12

Spring 2013 14

Emitted Radiationrsquos Color and Intensity Emitted Radiationrsquos Color and Intensity depend on Temperaturedepend on Temperature

Object

YouHeat LampCandle FlameBulb FilamentSunrsquos Surface

Temperature

~ 30 C~ 500 C~ 1700 C~ 2700 C~ 5500 C

Color

Infrared (invisible)Dull redDim orangeYellowBrilliant white

The hotter it gets the ldquobluerrdquo the emitted lightThe hotter it gets the more intense the radiation (more energy)

UCSD Physics 12

Spring 2013 15

ldquoldquoBlackbodyrdquo or Planck SpectrumBlackbodyrdquo or Planck Spectrum

UCSD Physics 12

Spring 2013 16

Same thing on logarithmic scaleSame thing on logarithmic scale

Sun peaks in visible band (05 microns) light bulbs at 1 m we at 10 m(note 0degC = 273degK 300degK = 27degC = 81degF)

UCSD Physics 12

Spring 2013 17

Okay but how much energyOkay but how much energy

bull The power given off of a surface in the form of light is The power given off of a surface in the form of light is proportional to the proportional to the fourth powerfourth power of temperature of temperature

F = F = TT44 in Watts per square meter in Watts per square meterndash the constant is numerically 56710-8 WordmK4m2

ndash easy to remember constant 5678

ndash temperature must be in Kelvinbull ordmK = ordmC + 273

bull ordmC = (59)(ordmF ndash32)

bull Example radiation from your bodyExample radiation from your body(567 10-8) (310)4 = 523 Watts per square meter

(if naked in the cold of space donrsquot let this happen to you)

UCSD Physics 12

Spring 2013 18

Radiant Energy continuedRadiant Energy continued

bull Example The sun is 5800Example The sun is 5800ordmK on its surface soordmK on its surface soF = T4 = (56710-8)(5800)4 = 64107 Wm2

Summing over entire surface area of sun gives 391026 W

bull Compare to total capacity of energy production on Compare to total capacity of energy production on earth 33earth 3310101212 W Wndash Single power plant typically 05ndash10 GW (109 W)

bull In earthly situations radiated power out partially In earthly situations radiated power out partially balanced by radiated power in from other sourcesbalanced by radiated power in from other sourcesndash Not 523 Wm2 in 70ordmF room more like 100 Wm2

bull goes like Th4 ndash Tc

4

Q

UCSD Physics 12

Spring 2013 19

And those are the major playershellipAnd those are the major playershellip

bull Wersquove now seen all the major energy players wersquoll Wersquove now seen all the major energy players wersquoll be discussing in this classbe discussing in this classndash work as force times distance

ndash kinetic energy (wind ocean currents)

ndash gravitational potential energy (hydroelectric tidal)

ndash chemical energy (fossil fuels batteries food biomass)

ndash heat energy (power plants space heating)

ndash mass-energy (nuclear sources sunrsquos energy)

ndash radiant energy (solar energy)

UCSD Physics 12

Spring 2013 20

AssignmentsAssignments

bull Homework 1 due April 12 in classHomework 1 due April 12 in classndash Chapter 1 problems plus online additions

bull see assignments link on web page for details

ndash donrsquot forget to show your workreasoning on the multiple choice

bull the answers alone do not suffice

bull Quiz 1 due Friday April 12 by midnightQuiz 1 due Friday April 12 by midnightndash TED will be up and quizzes available by Thursday

ndash 3 attempts permitted

ndash all numericalquantitative this week

UCSD Physics 12

Spring 2013 15

ldquoldquoBlackbodyrdquo or Planck SpectrumBlackbodyrdquo or Planck Spectrum

UCSD Physics 12

Spring 2013 16

Same thing on logarithmic scaleSame thing on logarithmic scale

Sun peaks in visible band (05 microns) light bulbs at 1 m we at 10 m(note 0degC = 273degK 300degK = 27degC = 81degF)

UCSD Physics 12

Spring 2013 17

Okay but how much energyOkay but how much energy

bull The power given off of a surface in the form of light is The power given off of a surface in the form of light is proportional to the proportional to the fourth powerfourth power of temperature of temperature

F = F = TT44 in Watts per square meter in Watts per square meterndash the constant is numerically 56710-8 WordmK4m2

ndash easy to remember constant 5678

ndash temperature must be in Kelvinbull ordmK = ordmC + 273

bull ordmC = (59)(ordmF ndash32)

bull Example radiation from your bodyExample radiation from your body(567 10-8) (310)4 = 523 Watts per square meter

(if naked in the cold of space donrsquot let this happen to you)

UCSD Physics 12

Spring 2013 18

Radiant Energy continuedRadiant Energy continued

bull Example The sun is 5800Example The sun is 5800ordmK on its surface soordmK on its surface soF = T4 = (56710-8)(5800)4 = 64107 Wm2

Summing over entire surface area of sun gives 391026 W

bull Compare to total capacity of energy production on Compare to total capacity of energy production on earth 33earth 3310101212 W Wndash Single power plant typically 05ndash10 GW (109 W)

bull In earthly situations radiated power out partially In earthly situations radiated power out partially balanced by radiated power in from other sourcesbalanced by radiated power in from other sourcesndash Not 523 Wm2 in 70ordmF room more like 100 Wm2

bull goes like Th4 ndash Tc

4

Q

UCSD Physics 12

Spring 2013 19

And those are the major playershellipAnd those are the major playershellip

bull Wersquove now seen all the major energy players wersquoll Wersquove now seen all the major energy players wersquoll be discussing in this classbe discussing in this classndash work as force times distance

ndash kinetic energy (wind ocean currents)

ndash gravitational potential energy (hydroelectric tidal)

ndash chemical energy (fossil fuels batteries food biomass)

ndash heat energy (power plants space heating)

ndash mass-energy (nuclear sources sunrsquos energy)

ndash radiant energy (solar energy)

UCSD Physics 12

Spring 2013 20

AssignmentsAssignments

bull Homework 1 due April 12 in classHomework 1 due April 12 in classndash Chapter 1 problems plus online additions

bull see assignments link on web page for details

ndash donrsquot forget to show your workreasoning on the multiple choice

bull the answers alone do not suffice

bull Quiz 1 due Friday April 12 by midnightQuiz 1 due Friday April 12 by midnightndash TED will be up and quizzes available by Thursday

ndash 3 attempts permitted

ndash all numericalquantitative this week

UCSD Physics 12

Spring 2013 16

Same thing on logarithmic scaleSame thing on logarithmic scale

Sun peaks in visible band (05 microns) light bulbs at 1 m we at 10 m(note 0degC = 273degK 300degK = 27degC = 81degF)

UCSD Physics 12

Spring 2013 17

Okay but how much energyOkay but how much energy

bull The power given off of a surface in the form of light is The power given off of a surface in the form of light is proportional to the proportional to the fourth powerfourth power of temperature of temperature

F = F = TT44 in Watts per square meter in Watts per square meterndash the constant is numerically 56710-8 WordmK4m2

ndash easy to remember constant 5678

ndash temperature must be in Kelvinbull ordmK = ordmC + 273

bull ordmC = (59)(ordmF ndash32)

bull Example radiation from your bodyExample radiation from your body(567 10-8) (310)4 = 523 Watts per square meter

(if naked in the cold of space donrsquot let this happen to you)

UCSD Physics 12

Spring 2013 18

Radiant Energy continuedRadiant Energy continued

bull Example The sun is 5800Example The sun is 5800ordmK on its surface soordmK on its surface soF = T4 = (56710-8)(5800)4 = 64107 Wm2

Summing over entire surface area of sun gives 391026 W

bull Compare to total capacity of energy production on Compare to total capacity of energy production on earth 33earth 3310101212 W Wndash Single power plant typically 05ndash10 GW (109 W)

bull In earthly situations radiated power out partially In earthly situations radiated power out partially balanced by radiated power in from other sourcesbalanced by radiated power in from other sourcesndash Not 523 Wm2 in 70ordmF room more like 100 Wm2

bull goes like Th4 ndash Tc

4

Q

UCSD Physics 12

Spring 2013 19

And those are the major playershellipAnd those are the major playershellip

bull Wersquove now seen all the major energy players wersquoll Wersquove now seen all the major energy players wersquoll be discussing in this classbe discussing in this classndash work as force times distance

ndash kinetic energy (wind ocean currents)

ndash gravitational potential energy (hydroelectric tidal)

ndash chemical energy (fossil fuels batteries food biomass)

ndash heat energy (power plants space heating)

ndash mass-energy (nuclear sources sunrsquos energy)

ndash radiant energy (solar energy)

UCSD Physics 12

Spring 2013 20

AssignmentsAssignments

bull Homework 1 due April 12 in classHomework 1 due April 12 in classndash Chapter 1 problems plus online additions

bull see assignments link on web page for details

ndash donrsquot forget to show your workreasoning on the multiple choice

bull the answers alone do not suffice

bull Quiz 1 due Friday April 12 by midnightQuiz 1 due Friday April 12 by midnightndash TED will be up and quizzes available by Thursday

ndash 3 attempts permitted

ndash all numericalquantitative this week

UCSD Physics 12

Spring 2013 17

Okay but how much energyOkay but how much energy

bull The power given off of a surface in the form of light is The power given off of a surface in the form of light is proportional to the proportional to the fourth powerfourth power of temperature of temperature

F = F = TT44 in Watts per square meter in Watts per square meterndash the constant is numerically 56710-8 WordmK4m2

ndash easy to remember constant 5678

ndash temperature must be in Kelvinbull ordmK = ordmC + 273

bull ordmC = (59)(ordmF ndash32)

bull Example radiation from your bodyExample radiation from your body(567 10-8) (310)4 = 523 Watts per square meter

(if naked in the cold of space donrsquot let this happen to you)

UCSD Physics 12

Spring 2013 18

Radiant Energy continuedRadiant Energy continued

bull Example The sun is 5800Example The sun is 5800ordmK on its surface soordmK on its surface soF = T4 = (56710-8)(5800)4 = 64107 Wm2

Summing over entire surface area of sun gives 391026 W

bull Compare to total capacity of energy production on Compare to total capacity of energy production on earth 33earth 3310101212 W Wndash Single power plant typically 05ndash10 GW (109 W)

bull In earthly situations radiated power out partially In earthly situations radiated power out partially balanced by radiated power in from other sourcesbalanced by radiated power in from other sourcesndash Not 523 Wm2 in 70ordmF room more like 100 Wm2

bull goes like Th4 ndash Tc

4

Q

UCSD Physics 12

Spring 2013 19

And those are the major playershellipAnd those are the major playershellip

bull Wersquove now seen all the major energy players wersquoll Wersquove now seen all the major energy players wersquoll be discussing in this classbe discussing in this classndash work as force times distance

ndash kinetic energy (wind ocean currents)

ndash gravitational potential energy (hydroelectric tidal)

ndash chemical energy (fossil fuels batteries food biomass)

ndash heat energy (power plants space heating)

ndash mass-energy (nuclear sources sunrsquos energy)

ndash radiant energy (solar energy)

UCSD Physics 12

Spring 2013 20

AssignmentsAssignments

bull Homework 1 due April 12 in classHomework 1 due April 12 in classndash Chapter 1 problems plus online additions

bull see assignments link on web page for details

ndash donrsquot forget to show your workreasoning on the multiple choice

bull the answers alone do not suffice

bull Quiz 1 due Friday April 12 by midnightQuiz 1 due Friday April 12 by midnightndash TED will be up and quizzes available by Thursday

ndash 3 attempts permitted

ndash all numericalquantitative this week

UCSD Physics 12

Spring 2013 18

Radiant Energy continuedRadiant Energy continued

bull Example The sun is 5800Example The sun is 5800ordmK on its surface soordmK on its surface soF = T4 = (56710-8)(5800)4 = 64107 Wm2

Summing over entire surface area of sun gives 391026 W

bull Compare to total capacity of energy production on Compare to total capacity of energy production on earth 33earth 3310101212 W Wndash Single power plant typically 05ndash10 GW (109 W)

bull In earthly situations radiated power out partially In earthly situations radiated power out partially balanced by radiated power in from other sourcesbalanced by radiated power in from other sourcesndash Not 523 Wm2 in 70ordmF room more like 100 Wm2

bull goes like Th4 ndash Tc

4

Q

UCSD Physics 12

Spring 2013 19

And those are the major playershellipAnd those are the major playershellip

bull Wersquove now seen all the major energy players wersquoll Wersquove now seen all the major energy players wersquoll be discussing in this classbe discussing in this classndash work as force times distance

ndash kinetic energy (wind ocean currents)

ndash gravitational potential energy (hydroelectric tidal)

ndash chemical energy (fossil fuels batteries food biomass)

ndash heat energy (power plants space heating)

ndash mass-energy (nuclear sources sunrsquos energy)

ndash radiant energy (solar energy)

UCSD Physics 12

Spring 2013 20

AssignmentsAssignments

bull Homework 1 due April 12 in classHomework 1 due April 12 in classndash Chapter 1 problems plus online additions

bull see assignments link on web page for details

ndash donrsquot forget to show your workreasoning on the multiple choice

bull the answers alone do not suffice

bull Quiz 1 due Friday April 12 by midnightQuiz 1 due Friday April 12 by midnightndash TED will be up and quizzes available by Thursday

ndash 3 attempts permitted

ndash all numericalquantitative this week

UCSD Physics 12

Spring 2013 19

And those are the major playershellipAnd those are the major playershellip

bull Wersquove now seen all the major energy players wersquoll Wersquove now seen all the major energy players wersquoll be discussing in this classbe discussing in this classndash work as force times distance

ndash kinetic energy (wind ocean currents)

ndash gravitational potential energy (hydroelectric tidal)

ndash chemical energy (fossil fuels batteries food biomass)

ndash heat energy (power plants space heating)

ndash mass-energy (nuclear sources sunrsquos energy)

ndash radiant energy (solar energy)

UCSD Physics 12

Spring 2013 20

AssignmentsAssignments

bull Homework 1 due April 12 in classHomework 1 due April 12 in classndash Chapter 1 problems plus online additions

bull see assignments link on web page for details

ndash donrsquot forget to show your workreasoning on the multiple choice

bull the answers alone do not suffice

bull Quiz 1 due Friday April 12 by midnightQuiz 1 due Friday April 12 by midnightndash TED will be up and quizzes available by Thursday

ndash 3 attempts permitted

ndash all numericalquantitative this week

UCSD Physics 12

Spring 2013 20

AssignmentsAssignments

bull Homework 1 due April 12 in classHomework 1 due April 12 in classndash Chapter 1 problems plus online additions

bull see assignments link on web page for details

ndash donrsquot forget to show your workreasoning on the multiple choice

bull the answers alone do not suffice

bull Quiz 1 due Friday April 12 by midnightQuiz 1 due Friday April 12 by midnightndash TED will be up and quizzes available by Thursday

ndash 3 attempts permitted

ndash all numericalquantitative this week