Physics 105 Physics for Decision Makers: The Global Energy Crisis

Physics 105 Physics for Decision Makers:The Global Energy CrisisLecture 6 Ozone, Cell Phones and ElectricityFall 2011

Physics 105 Fall 20111www.eia.govNew International Energy Outlook 2011 came out yesterday

World energy consumption increases by 53% between 2008 and 2035 with half of the increase attributed to China and India (last years estimate was 48%) Renewables are the worlds fastest-growing energy source, at 2.8% per year; renewables share of world energy grows to roughly 15% in 2035 Fossil fuels continue to supply almost 80% of world energy use in 2035

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September 11, 2010

Physics 105 Fall 2011Ozone - PolarO3Lowest value of ozone measured each year in the ozone hole.Global average ozone is about 300 Dobson units. Before 1980 ozone less than 200 Dobson units was rarely seen.

Physics 105 Fall 2011There is a lag time between emissions reduction and polar chlorine concentration because it takes some years for the lower atmospheric chlorofluorocarbons to reach the stratosphere and be broken up through action of ultraviolet solar radiation. The best estimate for the lifetime of CFC-11, for example, is about 50 years

Physics 105 Fall 2011Montreal ProtocolPerhaps the single most successful international agreement to date has been the Montreal Protocol. "-Kofi Annan, Former Secretary General of the United Nations Page 7

Physics 105 Fall 2011CFC Production and Concentrations

Physics 105 Fall 2011CFCsstart to decline

Physics 105 Fall 2011Ozone (temperate latitudes)

Physics 105 Fall 2011What lessons have we learned from Ozone?Physics 105 Fall 2011Cell Phones and Cancer Page 12

Physics 105 Fall 2011Do Cell Phones Cause Cancer?YesNoMaybe Page 13Physics 105 Fall 2011Electromagnetic Spectrum

Physics 105 Fall 2011Riding downhill to and from the Zoo Page 15

Physics 105 Fall 2011The Zoo Region

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Page 19Physics 105 Fall 2011Do Cell Phones Cause Cancer?YesNoMaybe Page 20Physics 105 Fall 2011Gaussian Distribution

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Page 22Physics 105 Fall 2011Probabilities (2 sided)

Page 23Since this is the chance of being outside n sigma, if you are looking for a positive effect the chance is as big. Physics 105 Fall 2011Scientific Discovery and TrialsWhen is it does a result constitute a discovery?It varies by fieldPhysics its generally considered evidence at 3 sigma(s) (1 chance in 700) and a discovery at 5 sigma (1 chance in 2 million)Often 95% confidence level is just a 2 sigma effect

How often will you exceed n sigma (s)?Depends on how many independent times you tryWhen there are lots of trials the probability goes up of exceeding some value Page 24Physics 105 Fall 2011Vaccine Risk Assessment

Page 25Physics 105 Fall 2011Michele Bachmann on the HPV Vaccine The Republican hopeful said a mother approached her following the debate and told her that her daughter became mentally retarded after receiving the HPV vaccine. But the American Academy of Pediatrics blasted Bachmann, saying the notion that the vaccine can cause retardation has "absolutely no scientific validity.She claimed the vaccine was dangerous during the debate with no causality conclusion whateverBesides what does it mean for a 12 or 13 year old to become retarded? Page 26

Physics 105 Fall 2011Electricity

Physics 105 Fall 2011Electric ForcesMatter is composed of particles with charge.Charge in electricity plays the role of mass in gravity.Unlike mass, charge may be positive or negativeThe unit of charge is the Coulomb. Matter is composed of electrons, protons and neutrons.Matter is held together via an electric force.The proton charge is e = 1.6x10-19 C.The electron charge is exactly -e.The neutron charge is 0.Neutrons are held in the nucleus by another (Nuclear or strong force)

Opposite charges attractLike charges repel

Physics 105 Fall 2011Which force is stronger between and electron and proton - Gravity or ElectricityThey are both about the sameElectricity is a 106 (a million) times strongGravity is a 106 (a million) times strongElectricity is a 1040 times strongerGravity is a 1040 times strongerIt depends on the distance apartPhysics 105 Fall 2011Electrostatic Force - Coulombs LawTwo charges, Q1 and Q2, separated by distance r exert a force on each other:

F = (kQ1Q2)/r2

k is a constant (9109Nm2/C2), Q is in Coulombs, r in metersOne unit of charge (proton) has Q = 1.610-19 CoulombsLooks a lot like Newtons gravitation in form - F = (Gm1m2) /r2Electron and proton attract each other 1040 times stronger electrically than gravitationally!Good thing charge is usually balanced!

Q1Q2rPhysics 105 Fall 2011Coulombs Law - qualitativeDouble one of the chargesforce doublesChange sign of one of the chargesforce changes directionChange sign of both chargesforce stays the sameDouble the distance between chargesforce four times weakerDouble both chargesforce four times stronger

F = (kQ1Q2)/r2Physics 105 Fall 2011Charge BalanceNeutral atoms are made of equal quantities of positive and negative chargesNeutral carbon has 6 protons, 6 electrons, (& 6 neutrons)Electrons can be stripped off of atomsElectrons occupy the vulnerable outskirts of atomsAn ion is a particle with non-zero chargeUsually charge flows in such a way as to maintain neutralityExcess positive charge attracts excess negative chargeYour body has 51028 positive charges and 51028 negative charges, balanced within millions or billions

Physics 105 Fall 2011Structure of the atomneutronprotonelectronPhysics 105 Fall 2011Fly in the cathedral

Gold atom nuclear radius : 7 X 10-15 melectron orbit radius: 1.3 X 10-10 mAtoms are almost all empty spacePhysics 105 Fall 2011Building BlocksProtons neutrons electronsatomsmoleculesSolids, liquids, gasesPhysics 105 Fall 2011 Conductors and Insulators In some materials (metals), some electrons get freed from their individual atoms and can move through the materialConductors e.g. Copper, Aluminum, Gold, Silver, Mercury,

In most materials, the electrons are bound to their nuclei and cannot freely flowInsulators e.g. rubber, plastics, ceramics, glass, gases

Physics 105 Fall 2011Is water an electrical insulator or conductorInsulatorConductorNeitherPhysics 105 Fall 2011

Physics 105 Fall 2011Induced ChargeCharge can also be coaxed to redistribute itself within an object++++++Charged rod approaches sphere+ charge attracted to charge in rod charge repelled by rodResult: Attraction!Physics 105 Fall 2011The Atom-+ NHydrogen AtomA Atom is the smallest form of an element. Atoms combine to form molecules that make up all matter. The term Electricity comes from the Greek word elektron, meaning: Amber. Amber is a fossil resin that Ancients rubbed with wool to produce static electricity. This was their way of shocking someone since they had no nylon carpet in their tents! Physics 105 Fall 2011Electric PotentialSeparate a positive charge from a negative charge and give it electric potential energy

Physics 105 Fall 2011Electric PotentialTo move electric charge against an electric force requires work.V W/QThe electric potential energy difference between two points is the work per Coulomb to move charge between the points and in measured in volts where 1 volt = 1 joule/coulomb

1.5v+-

e-Physics 105 Fall 2011ConductorsA conductor is a material (usually a metal such as copper) that allows electric current to pass easily. The current is made up of electrons. This is opposed to an insulator which prevents the flow of electricity through it. Charge moves rather freely in good conductors such as copper. A metal wire acts like a pipe for charge.In equilibrium, charge distributes itself around the surface such that there is no interior electric field and the entire conductor is at constant potential.

Physics 105 Fall 2011Basics CircuitsVoltage is the electrical force, or "pressure", that causes current to flow in a circuit. It is measured in VOLTS (V ). Voltage would be the force that is pushing the water (electrons) forward.

Current is the movement of electrical charge the flow of electrons through the electronic circuit. In our analogy, current would be the flow of water moving through the tube (wire).

Physics 105 Fall 2011Basic CircuitsCurrent direction is from positive to negative voltages Current (I) is the rate charge flowsI = Q/DtCurrent is measured in AMPERES (AMPS, A ) 1 amp = 1 coulomb / sResistance is anything that causes an opposition to the flow of electricity in a circuit. Resistance is used to control the amount of voltage and/or amperage in a circuit. Everything in the circuit causes a resistance (even wire).

Physics 105 Fall 2011ResistanceWhat happens in a resistor?Electrons cant flow freelyThey run into atoms and transfers energy to the atomsThe resistor heats upA light bulb is a resistor It gets so hot it glows

http://micro.magnet.fsu.edu/electromag/java/filamentresistance/index.htmlPhysics 105 Fall 2011What happens when you ski down a hill?You start with gravitational potential energy and some gets transformed into kinetic energy V=sqrt(2gh) -> h=300mV=78m/s=175mphAssuming you stop at the bottom where did the potential energy go?Heating and moving the snow

Physics 105 Fall 2011Circuits

Lift gain potentialSki down drop potentialPhysics 105 Fall 2011Ohms LawThe voltage drop across a resistance is equal to the current times the resistanceV = IR R = V/I I = V/RWork is V*Q Power is W/Dt =V Q/DtPower = VISame power with small current and large voltage or small voltage and large currentP = VI = I2R = V2/RLower resistance more power used

Light bulbPhysics 105 Fall 2011 AC/DC

Physics 105 Fall 2011AC/DC AC - Alternating Current

V or I DC - Direct Current

V or I Physics 105 Fall 2011The War of the Currents

Thomas Edison(DC)George Westinghouse and Nikola Tesla(AC)vs.Physics 105 Fall 2011 Two Competing technologiesEdisons DC system was original US standardWestinghouse licensed Teslas AC systems

Some bad blood - Tesla had worked for Edison, but felt cheated

DC had to be generated nearby, AC could go longer distances

Edison started a campaign to discourage use of ACHis technicians publicly electrocuted stray cats and dogs with ACHe secretly paid for the construction of the electric chair (AC) (even though he was opposed to capital punishment)They didnt use a high enough voltage - took two triesThey would have done better using an axe = WestinghousePhysics 105 Fall 2011 Two Competing technologiesUltimate executionTopsy the elephant - a Coney Island circus elephantHad killed 3 people and was sentenced to deathGave it cyanide (to be sure) and electrocutedEdison filmed the execution which was widely shown

Edison tried to get being electrocuted called getting westinghoused

In the end AC won out - easier to transmit over long distances

Physics 105 Fall 2011 Why is AC better? Remember Ohms Law and power dissipated:

P = I V = I2 R

Pgenerated = Ploss+ PdeliveredFor a given R of the transmission lines, less current means less power lost- use high V and low I -Physics 105 Fall 2011Why is AC better? It is easy to change the voltage of AC electricityStep-upStep-down

Use transformersTime varying current generates magnetic fieldsTime varying magnetic fields generate currents

Physics 105 Fall 2011Typical ACUS - 60 Hz (cycles/second)Europe 50 Hz

US - 120 VEurope - 220 V

TransmissionAround campus - 13,600 VAcross country - 115,000 to 500,000 VHigher V means lower I - less loss!Physics 105 Fall 2011 DC is still usedBatteries are DC

Many small devices use DC - look at your chargers

Do not need high currents, long distance transmission

Chargers convert 120 V AC into DC (typically 3- 15 V)

Physics 105 Fall 2011How much current does a 1200 W spaceheater use?1/12 Amp1/2 Amp5/6 Amp1 Amp10 Amp100 AmpPhysics 105 Fall 2011