Chapter 6 Section 8

Energy Consumption Cold Shower

HW PTG 68 p 686 1-8 Due Friday

bull Learning Objectivendash Calculate the energy

efficiency of electrical devices

bull Success Criteriandash Calculate the heat gained by

a sample of waterndash Calculate the electrical

energy converted into heat by a resistor

ndash Calculate the efficiency of a transformation of electrical energy to heat

ndash Explore the power ratings and energy consumption levels of a variety of electrical appliances

bull Do Nowndash 67 Quizndash LO and SC on new left

side pagendash WDYSWDYT p 678

bull Agendandash Do Nowndash Investigationndash Summary

What do you see

What do you think

bull The entire daily energy output of a Homes For Everyone (HFE) generator would not be enough to heat water for an average American family for a day

bull If an electrical heating coil (a type of resistor) were submerged in a container of water and if a current were to flow through the coil to make it hot what factors would affect the temperature increase of the water

Investigation 68

bull 1 ndash setup and measurements of water and coil

bull 2 Heat water for 10 minutes

bull While water heats set up notebook

Investigation 68

bull Recall that the heat gained by an object can be found using the equation

bull ΔQ = mcΔTndash ΔQ is a measure of heat

in joulesndash m is the mass of the

substance in gramsndash c is the specific heat of

the substance andndash ΔT is the change in

temperature in degrees Celsius

bull 3 ndash Calculate the heat gained using your data table and the specific heat value of418 JgdegC

Investigation 68

bull P=Et so E=Ptbull where E is energy

in joules (watt-seconds)

bull P is power in watts (joulessecond)

bull t is time in seconds

bull 4 - Calculate the energy from your experiment using this equation

bull Answer 4 a and 5b

Investigation 68

100inputenergy

outputenergy useful Efficiency

bull 5 ndash Calculate the efficiency using the equation above and answer 5a

Summary

bull Do you think the heated coil is very efficient Why or why not Provide evidence to support your claim

HW PTG 68 p 686 1-8bull Learning Objective

ndash Calculate the energy efficiency of electrical devices

bull Success Criteriandash Calculate the heat gained by

a sample of waterndash Calculate the electrical

energy converted into heat by a resistor

ndash Calculate the efficiency of a transformation of electrical energy to heat

ndash Explore the power ratings and energy consumption levels of a variety of electrical appliances

bull Do Nowndash List some ways to

make the foam cup setup more energy efficient

bull Agendandash Do Nowndash Investigationndash Summary

Physics Talk 68

bull What is a kilowatt-hour

bull 1 kilowatt-hour of energy power time

bull 1000W x 1 h = bull 1000W x 3600 sbull = 3600000 J

bull Thatrsquos a lot of joules

Physics Talk 68

bull What is heat bull Heat is the transfer of thermal energy

bull In order for an object to heat up there must be a source of thermal energy

bull When objects cool down the thermal energy is being transferred elsewhere

Physics Talk 68

bull How does a thermos work

bull A thermos creates a barrier to isolate the contents This means that the amount of energy in the thermos must stay relatively the same

bull Cold things stay cold (blocks thermal energy from leaving)

bull Hot things stay hot (traps thermal energy in)

Physics Talk 68

bull How do we measure a change in heat

bull ΔQ = mcΔTndash ΔQ is a measure of

heat in joulesndash m is the mass of the

substance in gramsndash c is the specific

heat of the substance and

ndash ΔT is the change in temperature in degrees Celsius

Physics Talk 68

bull Another method for calculating a change in heat

bull We know energy = power x timebull We also know power = voltage x currentbull This means energy = voltage x current x time

bull E = VItbull where E is the energy in joules (J)

bull V is the voltage in volts (V)bull I is the current in amperes (A)bull t is the time in seconds (s)

Sample Problem

bull A 12-V starter battery in a car supplies 48 A of current to the starter If the starter draws energy for 15 s how much energy does the starter use

bull Givenndash V = 12Vndash I = 48Andash t = 15s

bull Unknownndash Energy (E)

bull Toolndash E = VIt

bull Solutionndash E= 12V48A15sndash E = 8640 J

Canceling Units

Physics Talk 68

bull What happened to the missing energy in the experiment

bull Some of the heat could have been lost out of the cup into the thermometer or somewhere else The important thing is that it went somewhere because ENERGY IS NEVER DESTROYED

Physics Talk 68

bull What is the equation for efficiency

100inputenergy

outputenergy useful Efficiency

Essential Questions

bull P 684 WDYTNbull Questions p 685ndash What does it meanndash How do you knowndash Why do you

believendash Why should you

care

Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class

HW PTG 68 p 686 1-8 Due Friday

bull Learning Objectivendash Calculate the energy

efficiency of electrical devices

bull Success Criteriandash Calculate the heat gained by

a sample of waterndash Calculate the electrical

energy converted into heat by a resistor

ndash Calculate the efficiency of a transformation of electrical energy to heat

ndash Explore the power ratings and energy consumption levels of a variety of electrical appliances

bull Do Nowndash 67 Quizndash LO and SC on new left

side pagendash WDYSWDYT p 678

bull Agendandash Do Nowndash Investigationndash Summary

What do you see

What do you think

bull The entire daily energy output of a Homes For Everyone (HFE) generator would not be enough to heat water for an average American family for a day

bull If an electrical heating coil (a type of resistor) were submerged in a container of water and if a current were to flow through the coil to make it hot what factors would affect the temperature increase of the water

Investigation 68

bull 1 ndash setup and measurements of water and coil

bull 2 Heat water for 10 minutes

bull While water heats set up notebook

Investigation 68

bull Recall that the heat gained by an object can be found using the equation

bull ΔQ = mcΔTndash ΔQ is a measure of heat

in joulesndash m is the mass of the

substance in gramsndash c is the specific heat of

the substance andndash ΔT is the change in

temperature in degrees Celsius

bull 3 ndash Calculate the heat gained using your data table and the specific heat value of418 JgdegC

Investigation 68

bull P=Et so E=Ptbull where E is energy

in joules (watt-seconds)

bull P is power in watts (joulessecond)

bull t is time in seconds

bull 4 - Calculate the energy from your experiment using this equation

bull Answer 4 a and 5b

Investigation 68

100inputenergy

outputenergy useful Efficiency

bull 5 ndash Calculate the efficiency using the equation above and answer 5a

Summary

bull Do you think the heated coil is very efficient Why or why not Provide evidence to support your claim

HW PTG 68 p 686 1-8bull Learning Objective

ndash Calculate the energy efficiency of electrical devices

bull Success Criteriandash Calculate the heat gained by

a sample of waterndash Calculate the electrical

energy converted into heat by a resistor

ndash Calculate the efficiency of a transformation of electrical energy to heat

ndash Explore the power ratings and energy consumption levels of a variety of electrical appliances

bull Do Nowndash List some ways to

make the foam cup setup more energy efficient

bull Agendandash Do Nowndash Investigationndash Summary

Physics Talk 68

bull What is a kilowatt-hour

bull 1 kilowatt-hour of energy power time

bull 1000W x 1 h = bull 1000W x 3600 sbull = 3600000 J

bull Thatrsquos a lot of joules

Physics Talk 68

bull What is heat bull Heat is the transfer of thermal energy

bull In order for an object to heat up there must be a source of thermal energy

bull When objects cool down the thermal energy is being transferred elsewhere

Physics Talk 68

bull How does a thermos work

bull A thermos creates a barrier to isolate the contents This means that the amount of energy in the thermos must stay relatively the same

bull Cold things stay cold (blocks thermal energy from leaving)

bull Hot things stay hot (traps thermal energy in)

Physics Talk 68

bull How do we measure a change in heat

bull ΔQ = mcΔTndash ΔQ is a measure of

heat in joulesndash m is the mass of the

substance in gramsndash c is the specific

heat of the substance and

ndash ΔT is the change in temperature in degrees Celsius

Physics Talk 68

bull Another method for calculating a change in heat

bull We know energy = power x timebull We also know power = voltage x currentbull This means energy = voltage x current x time

bull E = VItbull where E is the energy in joules (J)

bull V is the voltage in volts (V)bull I is the current in amperes (A)bull t is the time in seconds (s)

Sample Problem

bull A 12-V starter battery in a car supplies 48 A of current to the starter If the starter draws energy for 15 s how much energy does the starter use

bull Givenndash V = 12Vndash I = 48Andash t = 15s

bull Unknownndash Energy (E)

bull Toolndash E = VIt

bull Solutionndash E= 12V48A15sndash E = 8640 J

Canceling Units

Physics Talk 68

bull What happened to the missing energy in the experiment

bull Some of the heat could have been lost out of the cup into the thermometer or somewhere else The important thing is that it went somewhere because ENERGY IS NEVER DESTROYED

Physics Talk 68

bull What is the equation for efficiency

100inputenergy

outputenergy useful Efficiency

Essential Questions

bull P 684 WDYTNbull Questions p 685ndash What does it meanndash How do you knowndash Why do you

believendash Why should you

care

Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class

What do you see

What do you think

bull The entire daily energy output of a Homes For Everyone (HFE) generator would not be enough to heat water for an average American family for a day

bull If an electrical heating coil (a type of resistor) were submerged in a container of water and if a current were to flow through the coil to make it hot what factors would affect the temperature increase of the water

Investigation 68

bull 1 ndash setup and measurements of water and coil

bull 2 Heat water for 10 minutes

bull While water heats set up notebook

Investigation 68

bull Recall that the heat gained by an object can be found using the equation

bull ΔQ = mcΔTndash ΔQ is a measure of heat

in joulesndash m is the mass of the

substance in gramsndash c is the specific heat of

the substance andndash ΔT is the change in

temperature in degrees Celsius

bull 3 ndash Calculate the heat gained using your data table and the specific heat value of418 JgdegC

Investigation 68

bull P=Et so E=Ptbull where E is energy

in joules (watt-seconds)

bull P is power in watts (joulessecond)

bull t is time in seconds

bull 4 - Calculate the energy from your experiment using this equation

bull Answer 4 a and 5b

Investigation 68

100inputenergy

outputenergy useful Efficiency

bull 5 ndash Calculate the efficiency using the equation above and answer 5a

Summary

bull Do you think the heated coil is very efficient Why or why not Provide evidence to support your claim

HW PTG 68 p 686 1-8bull Learning Objective

ndash Calculate the energy efficiency of electrical devices

bull Success Criteriandash Calculate the heat gained by

a sample of waterndash Calculate the electrical

energy converted into heat by a resistor

ndash Calculate the efficiency of a transformation of electrical energy to heat

ndash Explore the power ratings and energy consumption levels of a variety of electrical appliances

bull Do Nowndash List some ways to

make the foam cup setup more energy efficient

bull Agendandash Do Nowndash Investigationndash Summary

Physics Talk 68

bull What is a kilowatt-hour

bull 1 kilowatt-hour of energy power time

bull 1000W x 1 h = bull 1000W x 3600 sbull = 3600000 J

bull Thatrsquos a lot of joules

Physics Talk 68

bull What is heat bull Heat is the transfer of thermal energy

bull In order for an object to heat up there must be a source of thermal energy

bull When objects cool down the thermal energy is being transferred elsewhere

Physics Talk 68

bull How does a thermos work

bull A thermos creates a barrier to isolate the contents This means that the amount of energy in the thermos must stay relatively the same

bull Cold things stay cold (blocks thermal energy from leaving)

bull Hot things stay hot (traps thermal energy in)

Physics Talk 68

bull How do we measure a change in heat

bull ΔQ = mcΔTndash ΔQ is a measure of

heat in joulesndash m is the mass of the

substance in gramsndash c is the specific

heat of the substance and

ndash ΔT is the change in temperature in degrees Celsius

Physics Talk 68

bull Another method for calculating a change in heat

bull We know energy = power x timebull We also know power = voltage x currentbull This means energy = voltage x current x time

bull E = VItbull where E is the energy in joules (J)

bull V is the voltage in volts (V)bull I is the current in amperes (A)bull t is the time in seconds (s)

Sample Problem

bull A 12-V starter battery in a car supplies 48 A of current to the starter If the starter draws energy for 15 s how much energy does the starter use

bull Givenndash V = 12Vndash I = 48Andash t = 15s

bull Unknownndash Energy (E)

bull Toolndash E = VIt

bull Solutionndash E= 12V48A15sndash E = 8640 J

Canceling Units

Physics Talk 68

bull What happened to the missing energy in the experiment

bull Some of the heat could have been lost out of the cup into the thermometer or somewhere else The important thing is that it went somewhere because ENERGY IS NEVER DESTROYED

Physics Talk 68

bull What is the equation for efficiency

100inputenergy

outputenergy useful Efficiency

Essential Questions

bull P 684 WDYTNbull Questions p 685ndash What does it meanndash How do you knowndash Why do you

believendash Why should you

care

Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class

What do you think

bull The entire daily energy output of a Homes For Everyone (HFE) generator would not be enough to heat water for an average American family for a day

bull If an electrical heating coil (a type of resistor) were submerged in a container of water and if a current were to flow through the coil to make it hot what factors would affect the temperature increase of the water

Investigation 68

bull 1 ndash setup and measurements of water and coil

bull 2 Heat water for 10 minutes

bull While water heats set up notebook

Investigation 68

bull Recall that the heat gained by an object can be found using the equation

bull ΔQ = mcΔTndash ΔQ is a measure of heat

in joulesndash m is the mass of the

substance in gramsndash c is the specific heat of

the substance andndash ΔT is the change in

temperature in degrees Celsius

bull 3 ndash Calculate the heat gained using your data table and the specific heat value of418 JgdegC

Investigation 68

bull P=Et so E=Ptbull where E is energy

in joules (watt-seconds)

bull P is power in watts (joulessecond)

bull t is time in seconds

bull 4 - Calculate the energy from your experiment using this equation

bull Answer 4 a and 5b

Investigation 68

100inputenergy

outputenergy useful Efficiency

bull 5 ndash Calculate the efficiency using the equation above and answer 5a

Summary

bull Do you think the heated coil is very efficient Why or why not Provide evidence to support your claim

HW PTG 68 p 686 1-8bull Learning Objective

ndash Calculate the energy efficiency of electrical devices

bull Success Criteriandash Calculate the heat gained by

a sample of waterndash Calculate the electrical

energy converted into heat by a resistor

ndash Calculate the efficiency of a transformation of electrical energy to heat

ndash Explore the power ratings and energy consumption levels of a variety of electrical appliances

bull Do Nowndash List some ways to

make the foam cup setup more energy efficient

bull Agendandash Do Nowndash Investigationndash Summary

Physics Talk 68

bull What is a kilowatt-hour

bull 1 kilowatt-hour of energy power time

bull 1000W x 1 h = bull 1000W x 3600 sbull = 3600000 J

bull Thatrsquos a lot of joules

Physics Talk 68

bull What is heat bull Heat is the transfer of thermal energy

bull In order for an object to heat up there must be a source of thermal energy

bull When objects cool down the thermal energy is being transferred elsewhere

Physics Talk 68

bull How does a thermos work

bull A thermos creates a barrier to isolate the contents This means that the amount of energy in the thermos must stay relatively the same

bull Cold things stay cold (blocks thermal energy from leaving)

bull Hot things stay hot (traps thermal energy in)

Physics Talk 68

bull How do we measure a change in heat

bull ΔQ = mcΔTndash ΔQ is a measure of

heat in joulesndash m is the mass of the

substance in gramsndash c is the specific

heat of the substance and

ndash ΔT is the change in temperature in degrees Celsius

Physics Talk 68

bull Another method for calculating a change in heat

bull We know energy = power x timebull We also know power = voltage x currentbull This means energy = voltage x current x time

bull E = VItbull where E is the energy in joules (J)

bull V is the voltage in volts (V)bull I is the current in amperes (A)bull t is the time in seconds (s)

Sample Problem

bull A 12-V starter battery in a car supplies 48 A of current to the starter If the starter draws energy for 15 s how much energy does the starter use

bull Givenndash V = 12Vndash I = 48Andash t = 15s

bull Unknownndash Energy (E)

bull Toolndash E = VIt

bull Solutionndash E= 12V48A15sndash E = 8640 J

Canceling Units

Physics Talk 68

bull What happened to the missing energy in the experiment

bull Some of the heat could have been lost out of the cup into the thermometer or somewhere else The important thing is that it went somewhere because ENERGY IS NEVER DESTROYED

Physics Talk 68

bull What is the equation for efficiency

100inputenergy

outputenergy useful Efficiency

Essential Questions

bull P 684 WDYTNbull Questions p 685ndash What does it meanndash How do you knowndash Why do you

believendash Why should you

care

Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class

Investigation 68

bull 1 ndash setup and measurements of water and coil

bull 2 Heat water for 10 minutes

bull While water heats set up notebook

Investigation 68

bull Recall that the heat gained by an object can be found using the equation

bull ΔQ = mcΔTndash ΔQ is a measure of heat

in joulesndash m is the mass of the

substance in gramsndash c is the specific heat of

the substance andndash ΔT is the change in

temperature in degrees Celsius

bull 3 ndash Calculate the heat gained using your data table and the specific heat value of418 JgdegC

Investigation 68

bull P=Et so E=Ptbull where E is energy

in joules (watt-seconds)

bull P is power in watts (joulessecond)

bull t is time in seconds

bull 4 - Calculate the energy from your experiment using this equation

bull Answer 4 a and 5b

Investigation 68

100inputenergy

outputenergy useful Efficiency

bull 5 ndash Calculate the efficiency using the equation above and answer 5a

Summary

bull Do you think the heated coil is very efficient Why or why not Provide evidence to support your claim

HW PTG 68 p 686 1-8bull Learning Objective

ndash Calculate the energy efficiency of electrical devices

bull Success Criteriandash Calculate the heat gained by

a sample of waterndash Calculate the electrical

energy converted into heat by a resistor

ndash Calculate the efficiency of a transformation of electrical energy to heat

ndash Explore the power ratings and energy consumption levels of a variety of electrical appliances

bull Do Nowndash List some ways to

make the foam cup setup more energy efficient

bull Agendandash Do Nowndash Investigationndash Summary

Physics Talk 68

bull What is a kilowatt-hour

bull 1 kilowatt-hour of energy power time

bull 1000W x 1 h = bull 1000W x 3600 sbull = 3600000 J

bull Thatrsquos a lot of joules

Physics Talk 68

bull What is heat bull Heat is the transfer of thermal energy

bull In order for an object to heat up there must be a source of thermal energy

bull When objects cool down the thermal energy is being transferred elsewhere

Physics Talk 68

bull How does a thermos work

bull A thermos creates a barrier to isolate the contents This means that the amount of energy in the thermos must stay relatively the same

bull Cold things stay cold (blocks thermal energy from leaving)

bull Hot things stay hot (traps thermal energy in)

Physics Talk 68

bull How do we measure a change in heat

bull ΔQ = mcΔTndash ΔQ is a measure of

heat in joulesndash m is the mass of the

substance in gramsndash c is the specific

heat of the substance and

ndash ΔT is the change in temperature in degrees Celsius

Physics Talk 68

bull Another method for calculating a change in heat

bull We know energy = power x timebull We also know power = voltage x currentbull This means energy = voltage x current x time

bull E = VItbull where E is the energy in joules (J)

bull V is the voltage in volts (V)bull I is the current in amperes (A)bull t is the time in seconds (s)

Sample Problem

bull A 12-V starter battery in a car supplies 48 A of current to the starter If the starter draws energy for 15 s how much energy does the starter use

bull Givenndash V = 12Vndash I = 48Andash t = 15s

bull Unknownndash Energy (E)

bull Toolndash E = VIt

bull Solutionndash E= 12V48A15sndash E = 8640 J

Canceling Units

Physics Talk 68

bull What happened to the missing energy in the experiment

bull Some of the heat could have been lost out of the cup into the thermometer or somewhere else The important thing is that it went somewhere because ENERGY IS NEVER DESTROYED

Physics Talk 68

bull What is the equation for efficiency

100inputenergy

outputenergy useful Efficiency

Essential Questions

bull P 684 WDYTNbull Questions p 685ndash What does it meanndash How do you knowndash Why do you

believendash Why should you

care

Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class

Investigation 68

bull Recall that the heat gained by an object can be found using the equation

bull ΔQ = mcΔTndash ΔQ is a measure of heat

in joulesndash m is the mass of the

substance in gramsndash c is the specific heat of

the substance andndash ΔT is the change in

temperature in degrees Celsius

bull 3 ndash Calculate the heat gained using your data table and the specific heat value of418 JgdegC

Investigation 68

bull P=Et so E=Ptbull where E is energy

in joules (watt-seconds)

bull P is power in watts (joulessecond)

bull t is time in seconds

bull 4 - Calculate the energy from your experiment using this equation

bull Answer 4 a and 5b

Investigation 68

100inputenergy

outputenergy useful Efficiency

bull 5 ndash Calculate the efficiency using the equation above and answer 5a

Summary

bull Do you think the heated coil is very efficient Why or why not Provide evidence to support your claim

HW PTG 68 p 686 1-8bull Learning Objective

ndash Calculate the energy efficiency of electrical devices

bull Success Criteriandash Calculate the heat gained by

a sample of waterndash Calculate the electrical

energy converted into heat by a resistor

ndash Calculate the efficiency of a transformation of electrical energy to heat

ndash Explore the power ratings and energy consumption levels of a variety of electrical appliances

bull Do Nowndash List some ways to

make the foam cup setup more energy efficient

bull Agendandash Do Nowndash Investigationndash Summary

Physics Talk 68

bull What is a kilowatt-hour

bull 1 kilowatt-hour of energy power time

bull 1000W x 1 h = bull 1000W x 3600 sbull = 3600000 J

bull Thatrsquos a lot of joules

Physics Talk 68

bull What is heat bull Heat is the transfer of thermal energy

bull In order for an object to heat up there must be a source of thermal energy

bull When objects cool down the thermal energy is being transferred elsewhere

Physics Talk 68

bull How does a thermos work

bull A thermos creates a barrier to isolate the contents This means that the amount of energy in the thermos must stay relatively the same

bull Cold things stay cold (blocks thermal energy from leaving)

bull Hot things stay hot (traps thermal energy in)

Physics Talk 68

bull How do we measure a change in heat

bull ΔQ = mcΔTndash ΔQ is a measure of

heat in joulesndash m is the mass of the

substance in gramsndash c is the specific

heat of the substance and

ndash ΔT is the change in temperature in degrees Celsius

Physics Talk 68

bull Another method for calculating a change in heat

bull We know energy = power x timebull We also know power = voltage x currentbull This means energy = voltage x current x time

bull E = VItbull where E is the energy in joules (J)

bull V is the voltage in volts (V)bull I is the current in amperes (A)bull t is the time in seconds (s)

Sample Problem

bull A 12-V starter battery in a car supplies 48 A of current to the starter If the starter draws energy for 15 s how much energy does the starter use

bull Givenndash V = 12Vndash I = 48Andash t = 15s

bull Unknownndash Energy (E)

bull Toolndash E = VIt

bull Solutionndash E= 12V48A15sndash E = 8640 J

Canceling Units

Physics Talk 68

bull What happened to the missing energy in the experiment

bull Some of the heat could have been lost out of the cup into the thermometer or somewhere else The important thing is that it went somewhere because ENERGY IS NEVER DESTROYED

Physics Talk 68

bull What is the equation for efficiency

100inputenergy

outputenergy useful Efficiency

Essential Questions

bull P 684 WDYTNbull Questions p 685ndash What does it meanndash How do you knowndash Why do you

believendash Why should you

care

Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class

Investigation 68

bull P=Et so E=Ptbull where E is energy

in joules (watt-seconds)

bull P is power in watts (joulessecond)

bull t is time in seconds

bull 4 - Calculate the energy from your experiment using this equation

bull Answer 4 a and 5b

Investigation 68

100inputenergy

outputenergy useful Efficiency

bull 5 ndash Calculate the efficiency using the equation above and answer 5a

Summary

bull Do you think the heated coil is very efficient Why or why not Provide evidence to support your claim

HW PTG 68 p 686 1-8bull Learning Objective

ndash Calculate the energy efficiency of electrical devices

bull Success Criteriandash Calculate the heat gained by

a sample of waterndash Calculate the electrical

energy converted into heat by a resistor

ndash Calculate the efficiency of a transformation of electrical energy to heat

ndash Explore the power ratings and energy consumption levels of a variety of electrical appliances

bull Do Nowndash List some ways to

make the foam cup setup more energy efficient

bull Agendandash Do Nowndash Investigationndash Summary

Physics Talk 68

bull What is a kilowatt-hour

bull 1 kilowatt-hour of energy power time

bull 1000W x 1 h = bull 1000W x 3600 sbull = 3600000 J

bull Thatrsquos a lot of joules

Physics Talk 68

bull What is heat bull Heat is the transfer of thermal energy

bull In order for an object to heat up there must be a source of thermal energy

bull When objects cool down the thermal energy is being transferred elsewhere

Physics Talk 68

bull How does a thermos work

bull A thermos creates a barrier to isolate the contents This means that the amount of energy in the thermos must stay relatively the same

bull Cold things stay cold (blocks thermal energy from leaving)

bull Hot things stay hot (traps thermal energy in)

Physics Talk 68

bull How do we measure a change in heat

bull ΔQ = mcΔTndash ΔQ is a measure of

heat in joulesndash m is the mass of the

substance in gramsndash c is the specific

heat of the substance and

ndash ΔT is the change in temperature in degrees Celsius

Physics Talk 68

bull Another method for calculating a change in heat

bull We know energy = power x timebull We also know power = voltage x currentbull This means energy = voltage x current x time

bull E = VItbull where E is the energy in joules (J)

bull V is the voltage in volts (V)bull I is the current in amperes (A)bull t is the time in seconds (s)

Sample Problem

bull A 12-V starter battery in a car supplies 48 A of current to the starter If the starter draws energy for 15 s how much energy does the starter use

bull Givenndash V = 12Vndash I = 48Andash t = 15s

bull Unknownndash Energy (E)

bull Toolndash E = VIt

bull Solutionndash E= 12V48A15sndash E = 8640 J

Canceling Units

Physics Talk 68

bull What happened to the missing energy in the experiment

bull Some of the heat could have been lost out of the cup into the thermometer or somewhere else The important thing is that it went somewhere because ENERGY IS NEVER DESTROYED

Physics Talk 68

bull What is the equation for efficiency

100inputenergy

outputenergy useful Efficiency

Essential Questions

bull P 684 WDYTNbull Questions p 685ndash What does it meanndash How do you knowndash Why do you

believendash Why should you

care

Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class

Investigation 68

100inputenergy

outputenergy useful Efficiency

bull 5 ndash Calculate the efficiency using the equation above and answer 5a

Summary

bull Do you think the heated coil is very efficient Why or why not Provide evidence to support your claim

HW PTG 68 p 686 1-8bull Learning Objective

ndash Calculate the energy efficiency of electrical devices

bull Success Criteriandash Calculate the heat gained by

a sample of waterndash Calculate the electrical

energy converted into heat by a resistor

ndash Calculate the efficiency of a transformation of electrical energy to heat

ndash Explore the power ratings and energy consumption levels of a variety of electrical appliances

bull Do Nowndash List some ways to

make the foam cup setup more energy efficient

bull Agendandash Do Nowndash Investigationndash Summary

Physics Talk 68

bull What is a kilowatt-hour

bull 1 kilowatt-hour of energy power time

bull 1000W x 1 h = bull 1000W x 3600 sbull = 3600000 J

bull Thatrsquos a lot of joules

Physics Talk 68

bull What is heat bull Heat is the transfer of thermal energy

bull In order for an object to heat up there must be a source of thermal energy

bull When objects cool down the thermal energy is being transferred elsewhere

Physics Talk 68

bull How does a thermos work

bull A thermos creates a barrier to isolate the contents This means that the amount of energy in the thermos must stay relatively the same

bull Cold things stay cold (blocks thermal energy from leaving)

bull Hot things stay hot (traps thermal energy in)

Physics Talk 68

bull How do we measure a change in heat

bull ΔQ = mcΔTndash ΔQ is a measure of

heat in joulesndash m is the mass of the

substance in gramsndash c is the specific

heat of the substance and

ndash ΔT is the change in temperature in degrees Celsius

Physics Talk 68

bull Another method for calculating a change in heat

bull We know energy = power x timebull We also know power = voltage x currentbull This means energy = voltage x current x time

bull E = VItbull where E is the energy in joules (J)

bull V is the voltage in volts (V)bull I is the current in amperes (A)bull t is the time in seconds (s)

Sample Problem

bull A 12-V starter battery in a car supplies 48 A of current to the starter If the starter draws energy for 15 s how much energy does the starter use

bull Givenndash V = 12Vndash I = 48Andash t = 15s

bull Unknownndash Energy (E)

bull Toolndash E = VIt

bull Solutionndash E= 12V48A15sndash E = 8640 J

Canceling Units

Physics Talk 68

bull What happened to the missing energy in the experiment

bull Some of the heat could have been lost out of the cup into the thermometer or somewhere else The important thing is that it went somewhere because ENERGY IS NEVER DESTROYED

Physics Talk 68

bull What is the equation for efficiency

100inputenergy

outputenergy useful Efficiency

Essential Questions

bull P 684 WDYTNbull Questions p 685ndash What does it meanndash How do you knowndash Why do you

believendash Why should you

care

Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class

Summary

bull Do you think the heated coil is very efficient Why or why not Provide evidence to support your claim

HW PTG 68 p 686 1-8bull Learning Objective

ndash Calculate the energy efficiency of electrical devices

bull Success Criteriandash Calculate the heat gained by

a sample of waterndash Calculate the electrical

energy converted into heat by a resistor

ndash Calculate the efficiency of a transformation of electrical energy to heat

ndash Explore the power ratings and energy consumption levels of a variety of electrical appliances

bull Do Nowndash List some ways to

make the foam cup setup more energy efficient

bull Agendandash Do Nowndash Investigationndash Summary

Physics Talk 68

bull What is a kilowatt-hour

bull 1 kilowatt-hour of energy power time

bull 1000W x 1 h = bull 1000W x 3600 sbull = 3600000 J

bull Thatrsquos a lot of joules

Physics Talk 68

bull What is heat bull Heat is the transfer of thermal energy

bull In order for an object to heat up there must be a source of thermal energy

bull When objects cool down the thermal energy is being transferred elsewhere

Physics Talk 68

bull How does a thermos work

bull A thermos creates a barrier to isolate the contents This means that the amount of energy in the thermos must stay relatively the same

bull Cold things stay cold (blocks thermal energy from leaving)

bull Hot things stay hot (traps thermal energy in)

Physics Talk 68

bull How do we measure a change in heat

bull ΔQ = mcΔTndash ΔQ is a measure of

heat in joulesndash m is the mass of the

substance in gramsndash c is the specific

heat of the substance and

ndash ΔT is the change in temperature in degrees Celsius

Physics Talk 68

bull Another method for calculating a change in heat

bull We know energy = power x timebull We also know power = voltage x currentbull This means energy = voltage x current x time

bull E = VItbull where E is the energy in joules (J)

bull V is the voltage in volts (V)bull I is the current in amperes (A)bull t is the time in seconds (s)

Sample Problem

bull A 12-V starter battery in a car supplies 48 A of current to the starter If the starter draws energy for 15 s how much energy does the starter use

bull Givenndash V = 12Vndash I = 48Andash t = 15s

bull Unknownndash Energy (E)

bull Toolndash E = VIt

bull Solutionndash E= 12V48A15sndash E = 8640 J

Canceling Units

Physics Talk 68

bull What happened to the missing energy in the experiment

bull Some of the heat could have been lost out of the cup into the thermometer or somewhere else The important thing is that it went somewhere because ENERGY IS NEVER DESTROYED

Physics Talk 68

bull What is the equation for efficiency

100inputenergy

outputenergy useful Efficiency

Essential Questions

bull P 684 WDYTNbull Questions p 685ndash What does it meanndash How do you knowndash Why do you

believendash Why should you

care

Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class

HW PTG 68 p 686 1-8bull Learning Objective

ndash Calculate the energy efficiency of electrical devices

bull Success Criteriandash Calculate the heat gained by

a sample of waterndash Calculate the electrical

energy converted into heat by a resistor

ndash Calculate the efficiency of a transformation of electrical energy to heat

ndash Explore the power ratings and energy consumption levels of a variety of electrical appliances

bull Do Nowndash List some ways to

make the foam cup setup more energy efficient

bull Agendandash Do Nowndash Investigationndash Summary

Physics Talk 68

bull What is a kilowatt-hour

bull 1 kilowatt-hour of energy power time

bull 1000W x 1 h = bull 1000W x 3600 sbull = 3600000 J

bull Thatrsquos a lot of joules

Physics Talk 68

bull What is heat bull Heat is the transfer of thermal energy

bull In order for an object to heat up there must be a source of thermal energy

bull When objects cool down the thermal energy is being transferred elsewhere

Physics Talk 68

bull How does a thermos work

bull A thermos creates a barrier to isolate the contents This means that the amount of energy in the thermos must stay relatively the same

bull Cold things stay cold (blocks thermal energy from leaving)

bull Hot things stay hot (traps thermal energy in)

Physics Talk 68

bull How do we measure a change in heat

bull ΔQ = mcΔTndash ΔQ is a measure of

heat in joulesndash m is the mass of the

substance in gramsndash c is the specific

heat of the substance and

ndash ΔT is the change in temperature in degrees Celsius

Physics Talk 68

bull Another method for calculating a change in heat

bull We know energy = power x timebull We also know power = voltage x currentbull This means energy = voltage x current x time

bull E = VItbull where E is the energy in joules (J)

bull V is the voltage in volts (V)bull I is the current in amperes (A)bull t is the time in seconds (s)

Sample Problem

bull A 12-V starter battery in a car supplies 48 A of current to the starter If the starter draws energy for 15 s how much energy does the starter use

bull Givenndash V = 12Vndash I = 48Andash t = 15s

bull Unknownndash Energy (E)

bull Toolndash E = VIt

bull Solutionndash E= 12V48A15sndash E = 8640 J

Canceling Units

Physics Talk 68

bull What happened to the missing energy in the experiment

bull Some of the heat could have been lost out of the cup into the thermometer or somewhere else The important thing is that it went somewhere because ENERGY IS NEVER DESTROYED

Physics Talk 68

bull What is the equation for efficiency

100inputenergy

outputenergy useful Efficiency

Essential Questions

bull P 684 WDYTNbull Questions p 685ndash What does it meanndash How do you knowndash Why do you

believendash Why should you

care

Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class

Physics Talk 68

bull What is a kilowatt-hour

bull 1 kilowatt-hour of energy power time

bull 1000W x 1 h = bull 1000W x 3600 sbull = 3600000 J

bull Thatrsquos a lot of joules

Physics Talk 68

bull What is heat bull Heat is the transfer of thermal energy

bull In order for an object to heat up there must be a source of thermal energy

bull When objects cool down the thermal energy is being transferred elsewhere

Physics Talk 68

bull How does a thermos work

bull A thermos creates a barrier to isolate the contents This means that the amount of energy in the thermos must stay relatively the same

bull Cold things stay cold (blocks thermal energy from leaving)

bull Hot things stay hot (traps thermal energy in)

Physics Talk 68

bull How do we measure a change in heat

bull ΔQ = mcΔTndash ΔQ is a measure of

heat in joulesndash m is the mass of the

substance in gramsndash c is the specific

heat of the substance and

ndash ΔT is the change in temperature in degrees Celsius

Physics Talk 68

bull Another method for calculating a change in heat

bull We know energy = power x timebull We also know power = voltage x currentbull This means energy = voltage x current x time

bull E = VItbull where E is the energy in joules (J)

bull V is the voltage in volts (V)bull I is the current in amperes (A)bull t is the time in seconds (s)

Sample Problem

bull A 12-V starter battery in a car supplies 48 A of current to the starter If the starter draws energy for 15 s how much energy does the starter use

bull Givenndash V = 12Vndash I = 48Andash t = 15s

bull Unknownndash Energy (E)

bull Toolndash E = VIt

bull Solutionndash E= 12V48A15sndash E = 8640 J

Canceling Units

Physics Talk 68

bull What happened to the missing energy in the experiment

bull Some of the heat could have been lost out of the cup into the thermometer or somewhere else The important thing is that it went somewhere because ENERGY IS NEVER DESTROYED

Physics Talk 68

bull What is the equation for efficiency

100inputenergy

outputenergy useful Efficiency

Essential Questions

bull P 684 WDYTNbull Questions p 685ndash What does it meanndash How do you knowndash Why do you

believendash Why should you

care

Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class

Physics Talk 68

bull What is heat bull Heat is the transfer of thermal energy

bull In order for an object to heat up there must be a source of thermal energy

bull When objects cool down the thermal energy is being transferred elsewhere

Physics Talk 68

bull How does a thermos work

bull A thermos creates a barrier to isolate the contents This means that the amount of energy in the thermos must stay relatively the same

bull Cold things stay cold (blocks thermal energy from leaving)

bull Hot things stay hot (traps thermal energy in)

Physics Talk 68

bull How do we measure a change in heat

bull ΔQ = mcΔTndash ΔQ is a measure of

heat in joulesndash m is the mass of the

substance in gramsndash c is the specific

heat of the substance and

ndash ΔT is the change in temperature in degrees Celsius

Physics Talk 68

bull Another method for calculating a change in heat

bull We know energy = power x timebull We also know power = voltage x currentbull This means energy = voltage x current x time

bull E = VItbull where E is the energy in joules (J)

bull V is the voltage in volts (V)bull I is the current in amperes (A)bull t is the time in seconds (s)

Sample Problem

bull A 12-V starter battery in a car supplies 48 A of current to the starter If the starter draws energy for 15 s how much energy does the starter use

bull Givenndash V = 12Vndash I = 48Andash t = 15s

bull Unknownndash Energy (E)

bull Toolndash E = VIt

bull Solutionndash E= 12V48A15sndash E = 8640 J

Canceling Units

Physics Talk 68

bull What happened to the missing energy in the experiment

bull Some of the heat could have been lost out of the cup into the thermometer or somewhere else The important thing is that it went somewhere because ENERGY IS NEVER DESTROYED

Physics Talk 68

bull What is the equation for efficiency

100inputenergy

outputenergy useful Efficiency

Essential Questions

bull P 684 WDYTNbull Questions p 685ndash What does it meanndash How do you knowndash Why do you

believendash Why should you

care

Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class

Physics Talk 68

bull How does a thermos work

bull A thermos creates a barrier to isolate the contents This means that the amount of energy in the thermos must stay relatively the same

bull Cold things stay cold (blocks thermal energy from leaving)

bull Hot things stay hot (traps thermal energy in)

Physics Talk 68

bull How do we measure a change in heat

bull ΔQ = mcΔTndash ΔQ is a measure of

heat in joulesndash m is the mass of the

substance in gramsndash c is the specific

heat of the substance and

ndash ΔT is the change in temperature in degrees Celsius

Physics Talk 68

bull Another method for calculating a change in heat

bull We know energy = power x timebull We also know power = voltage x currentbull This means energy = voltage x current x time

bull E = VItbull where E is the energy in joules (J)

bull V is the voltage in volts (V)bull I is the current in amperes (A)bull t is the time in seconds (s)

Sample Problem

bull A 12-V starter battery in a car supplies 48 A of current to the starter If the starter draws energy for 15 s how much energy does the starter use

bull Givenndash V = 12Vndash I = 48Andash t = 15s

bull Unknownndash Energy (E)

bull Toolndash E = VIt

bull Solutionndash E= 12V48A15sndash E = 8640 J

Canceling Units

Physics Talk 68

bull What happened to the missing energy in the experiment

bull Some of the heat could have been lost out of the cup into the thermometer or somewhere else The important thing is that it went somewhere because ENERGY IS NEVER DESTROYED

Physics Talk 68

bull What is the equation for efficiency

100inputenergy

outputenergy useful Efficiency

Essential Questions

bull P 684 WDYTNbull Questions p 685ndash What does it meanndash How do you knowndash Why do you

believendash Why should you

care

Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class

Physics Talk 68

bull How do we measure a change in heat

bull ΔQ = mcΔTndash ΔQ is a measure of

heat in joulesndash m is the mass of the

substance in gramsndash c is the specific

heat of the substance and

ndash ΔT is the change in temperature in degrees Celsius

Physics Talk 68

bull Another method for calculating a change in heat

bull We know energy = power x timebull We also know power = voltage x currentbull This means energy = voltage x current x time

bull E = VItbull where E is the energy in joules (J)

bull V is the voltage in volts (V)bull I is the current in amperes (A)bull t is the time in seconds (s)

Sample Problem

bull A 12-V starter battery in a car supplies 48 A of current to the starter If the starter draws energy for 15 s how much energy does the starter use

bull Givenndash V = 12Vndash I = 48Andash t = 15s

bull Unknownndash Energy (E)

bull Toolndash E = VIt

bull Solutionndash E= 12V48A15sndash E = 8640 J

Canceling Units

Physics Talk 68

bull What happened to the missing energy in the experiment

bull Some of the heat could have been lost out of the cup into the thermometer or somewhere else The important thing is that it went somewhere because ENERGY IS NEVER DESTROYED

Physics Talk 68

bull What is the equation for efficiency

100inputenergy

outputenergy useful Efficiency

Essential Questions

bull P 684 WDYTNbull Questions p 685ndash What does it meanndash How do you knowndash Why do you

believendash Why should you

care

Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class

Physics Talk 68

bull Another method for calculating a change in heat

bull We know energy = power x timebull We also know power = voltage x currentbull This means energy = voltage x current x time

bull E = VItbull where E is the energy in joules (J)

bull V is the voltage in volts (V)bull I is the current in amperes (A)bull t is the time in seconds (s)

Sample Problem

bull A 12-V starter battery in a car supplies 48 A of current to the starter If the starter draws energy for 15 s how much energy does the starter use

bull Givenndash V = 12Vndash I = 48Andash t = 15s

bull Unknownndash Energy (E)

bull Toolndash E = VIt

bull Solutionndash E= 12V48A15sndash E = 8640 J

Canceling Units

Physics Talk 68

bull What happened to the missing energy in the experiment

bull Some of the heat could have been lost out of the cup into the thermometer or somewhere else The important thing is that it went somewhere because ENERGY IS NEVER DESTROYED

Physics Talk 68

bull What is the equation for efficiency

100inputenergy

outputenergy useful Efficiency

Essential Questions

bull P 684 WDYTNbull Questions p 685ndash What does it meanndash How do you knowndash Why do you

believendash Why should you

care

Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class

Sample Problem

bull A 12-V starter battery in a car supplies 48 A of current to the starter If the starter draws energy for 15 s how much energy does the starter use

bull Givenndash V = 12Vndash I = 48Andash t = 15s

bull Unknownndash Energy (E)

bull Toolndash E = VIt

bull Solutionndash E= 12V48A15sndash E = 8640 J

Canceling Units

Physics Talk 68

bull What happened to the missing energy in the experiment

bull Some of the heat could have been lost out of the cup into the thermometer or somewhere else The important thing is that it went somewhere because ENERGY IS NEVER DESTROYED

Physics Talk 68

bull What is the equation for efficiency

100inputenergy

outputenergy useful Efficiency

Essential Questions

bull P 684 WDYTNbull Questions p 685ndash What does it meanndash How do you knowndash Why do you

believendash Why should you

care

Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class

Canceling Units

Physics Talk 68

bull What happened to the missing energy in the experiment

bull Some of the heat could have been lost out of the cup into the thermometer or somewhere else The important thing is that it went somewhere because ENERGY IS NEVER DESTROYED

Physics Talk 68

bull What is the equation for efficiency

100inputenergy

outputenergy useful Efficiency

Essential Questions

bull P 684 WDYTNbull Questions p 685ndash What does it meanndash How do you knowndash Why do you

believendash Why should you

care

Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class

Physics Talk 68

bull What happened to the missing energy in the experiment

bull Some of the heat could have been lost out of the cup into the thermometer or somewhere else The important thing is that it went somewhere because ENERGY IS NEVER DESTROYED

Physics Talk 68

bull What is the equation for efficiency

100inputenergy

outputenergy useful Efficiency

Essential Questions

bull P 684 WDYTNbull Questions p 685ndash What does it meanndash How do you knowndash Why do you

believendash Why should you

care

Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class

Physics Talk 68

bull What is the equation for efficiency

100inputenergy

outputenergy useful Efficiency

Essential Questions

bull P 684 WDYTNbull Questions p 685ndash What does it meanndash How do you knowndash Why do you

believendash Why should you

care

Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class

Essential Questions

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Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class

Physics To Go 5-8 as a class

• Chapter 6 Section 8
• HW PTG 68 p 686 1-8 Due Friday
• What do you see
• What do you think
• Investigation 68
• Investigation 68 (2)
• Investigation 68 (3)
• Investigation 68 (4)
• Summary
• HW PTG 68 p 686 1-8
• Physics Talk 68
• Physics Talk 68 (2)
• Physics Talk 68 (3)
• Physics Talk 68 (4)
• Physics Talk 68 (5)
• Sample Problem
• Canceling Units
• Physics Talk 68 (6)
• Physics Talk 68 (7)
• Essential Questions
• Physics To Go 5-8 as a class