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Physics 105 Physics for Decision Makers: The Global Energy Crisis

Fall 2 011. Physics 105 Physics for Decision Makers: The Global Energy Crisis. Lecture 17 Midterm Review. The midterm exam. Next Tuesday You are allowed one side 8 1/2” x 11” page of notes Bring a calculator if you want (not required) Format: short answer questions

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Physics 105 Physics for Decision Makers: The Global Energy Crisis

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  1. Fall 2011 Physics 105 Physics for Decision Makers:The Global Energy Crisis Lecture 17 Midterm Review

  2. The midterm exam Next Tuesday You are allowed one side 8 1/2” x 11” page of notes Bring a calculator if you want (not required) Format: short answer questions Some quantitative/estimation questions I will curve the exam No one can write a (new) exam and guarantee that an 81% is a B and a 79% a C. The exam can be curved both up or down

  3. The midterm exam I do NOT expect you to memorize formulas Formulas all will follow from dimensions of quantities I do NOT expect you to memorize statistics but you might want to note down key numbers I DO expect you to know “big picture” facts The US has a large reserve of coal, but very little oil I DO expect you to know important concepts Exponential growth, tragedy of the commons, peak oil… Studying Lecture notes Homework Discussion questions/projects On-line media

  4. Exam Today’s lecture will review some concepts Note: There are no absences permitted for the exam. Only exceptions: Health - requires doctor’s note University approved absence (requires documentation)

  5. How my first car caused the war in Iraq A bad car Page 5

  6. Ralph Nader Page 6

  7. Florida 2000 The Ballot Page 7

  8. Summer 1973 – Datsun (Nissan) 1200

  9. PHYSICS 105 Mid-term topics Energy - concepts of energy, work, power; potential/kinetic energy; units (W, J, Wh) Population - exponential growth; international trends Tragedy of the Commons - examples of commons; how to prevent Tragedy Ozone hole- source of problem (CFCs), potential impact; solution (ban); timescale Electricity - Ohm’s Law; AC vs. DC Thermodynamics - temperature; 1st law; 2nd law; entropy; heat engine; Carnot efficiency ElectricalSupply - electric grid; peak power; storage Fossil Fuels - source of fossil fuels; world trends; peak oil Pollution – Linear no thesholdvs non-linear effects, sources of pollution, fracking Transportation – Energy usage in transportation, hybrids, plug-in electrics, fuel economy

  10. My TV uses 100 W of power when on. I watch TV 4 hours per day. My daily energy usage is: 100 W 100 Wh 400 W 400 Wh 0.4 kWh 400 J

  11. My computer uses 360 W of power when on. The current my computer draws (@120V) is about: 1 amp 3 joules 3 amps 36 amps 360 W 0.36 kW 360 J

  12. Electricity costs $0.10 per kWh. How much does it cost to run a 100 W computer 10 hours per day for 10 days? $0.10 $1.00 $10.00 $100.00 $1000.00

  13. A perfect heat engine runs between two temperature reservoirs with temperatures T1 = 227 deg. C, and T2 = 127 deg C. What is its efficiency? 1% 10% 20% 40% 60% 100% You may need  = (T1-T2)/T1 T(K) = 273 + T(deg C)

  14. You make $100 a week. You are given a raise of 10% per year. How long will it take for your salary to double? 5 years 7 years 10 years Page 14

  15. You make $100 a week. You are given a raise of 10% per year. How much will you be making in 3 years? $130 $133 $135 $137 $140 Page 15

  16. If gas is $4/gal how much does the average American family spend on gas a year $1,000 $2,000 $3,000 $4,000 $5,000 $6,000 $8,000 $10,000 Page 16

  17. You are the CEO of a large on-line book selling company. Think of three energy related changes you could make that would both save energy and make money: What are the major changes that peak oil imply? Why are population dynamics relevant to energy supply and usage. Why did Tesla win and we use AC electrical power supply? Name three examples of heat engines. Give three examples of the tragedy of the commons and suggest solutions What was causing disappearing Ozone – why is this bad How can you reduce the heat loss from your house – explain in terms of the heat transfer Page 17

  18. What does Peak oil mean? Is it possible to have reached peak oil and still have lots of oil in the ground? What is Fracking and why do people do it? What is wrong with fracking? What is a linear no-threshold model? What are the alternatives? Why is the advantage of burning low-sulfur coal? Why does the EPA restrict sulfur emissions? Page 18

  19. What are the advantages of hybrid like the Prius over a regular car? What are the advantages of a plug-in hybrid like the Chevy Volt over a regular hybrid like the Prius? Page 19

  20. What is the energy source of a Prius? Gasoline Electricity Either Page 20

  21. What is the energy source of a Volt? Gasoline Electricity Either Page 21

  22. A 100kg student runs up a 5m hill in 10s What is the power the student is putting out? 50W 100W 250W 500W 50J 100J 250J 500J Assume g=10m/s2 Page 22

  23. For the student in the previous problem Estimate how much power he was using? 100W .5kW 1kW 2.5kW 5kW 500W Where does the extra energy go? Page 23

  24. The following is a selection of slides from previous lectures that emphasize the main points. If something appears here it does not necessarily mean that it will be on the exam. If it does not appear here that does not mean it will not be on the exam.

  25. Energy and Power Energy: the capacity to do work Work = force X distance Power: energy per time

  26. Energy/ Power Units – know the difference Joule = 1 kg m2/s2- Metric unit of energy Calorie (food) = 1 kcal = 1,000 calories = 4186 J 1 kcal (Calorie) is the equivalent energy to a 100w light bulb on for about 7 minutes BTU (British Thermal Unit) = energy to raise temperature of 1 lb of water by one degree F= 1,055 J = 0.25 Kcal Watt is J/s kWh = 1000 Joule/s for one hour = 3,600,000 J = 3.6 MJ Power = I (current) x V (voltage) -> 1 amp x 1 Volt = 1W Page 26

  27. Work • In physics, the definition of work is the application of a force through a distance • W = F·d • W is the work done • F is the force applied • d is the distance through which the force acts • Only the force that acts in the direction of motion counts towards work • Kinetic energy : Ekin= 1/2 m v2 • Work-Kinetic Energy Theorem:ΔEkin = Wnet

  28. A gallon of gasoline contains 130MJ of energy • How much would it cost to by the equivalent amount energy at $0.15 at kWh? • 1kWh= 1000Jx 3600s = 3.6x 106J =3.6MJ • (Or From the back of the exam – 1kWh =3.6 x 106J) • 130MJ/(3.6MJ/kWh = 36.1 kWh • 36.1kWh *$0.15/kWh = $5.41 • So why do we want to have a plug-in car? Page 28

  29. Estimates of Human Population Green revolution Industrial revolution Fire, tool-making

  30. World Population

  31. Tragedy of the Commons • Garrett Hardin 1968 • Article is on ELMS • A commons is an open spaceavailable to all • Hypothetical case of 10 dairy farmers using the land • In hard times everyone has a few cows and there is plenty of grass for all • As things improve we assume the that eventually we get 20 cows each (total 200 cows) and we have reached the carrying capacity of the land

  32. Tragedy of the Commons • What should a rational farmer do? • If he adds a cow he gets the benefit of another cow • However all the cows including his 21 now only get 200/201 (99.5%) of the nutrition it needs produce a full amount of milk • Mathematically lets say his benefit is +1 from the extra cow but each cow loses about 0.5% so he loses ~10% of one cow so his net profit from adding the cow is 9/10 of a cow • So he should do it • And so should everyone else • What happens next?

  33. How do we deal with T.o.t.C? Privatization If I own the land, it is in my interest to adjust the number of cows to prevent catastrophe Regulation An organization (usually governmental) set rules to make sure catastrophe does not happen

  34. Ozone, Oxygen and Life

  35. Ozone Absorbtion of UV

  36. Ozone Depleting Substances • Chlorofluorocarbons (CFCs) • contain: Cl, F, C • long-lived, non-toxic, non-corrosive, and non-flammable • Great as propellants • in 1960s used in refrigerators, air conditioners, spray cans, solvents, foams • The Problem was they were found to migrate to the upper atmosphere where they would break down and catalyze the destruction of Ozone. Fridges used to use ammonia

  37. Ozone Hole • Largest Antarctic ozone hole ever recorded (Sept. 2006)

  38. Ozone Chronology 1978 US bans nonessential aerosols (Canada, Norway, and Sweden) 1979 Germany hosts second UNEP meeting 1981 UNEP council recommends convention Reagan/Gorsuch/Hodel; DuPont discontinues research on CFCs alternatives 1982-85 working group meetings 1985 Vienna Convention British scientists publish Antarctic data 1987 Montreal Protocol: 50% reduction CFCs below 1986 by 2000)

  39. Conductors and Insulators • In some materials (metals), some electrons get freed from their individual atoms and can move through the material • Conductors e.g. Copper, Aluminum, Gold, Silver, Mercury,… • In most materials, the electrons are bound to their nuclei and cannot freely flow • Insulators e.g. rubber, plastics, ceramics, glass, gases

  40. AC/DC • AC - Alternating Current V or I • DC - Direct Current V or I

  41. The Zeroth Law of Thermodynamics • Temperature - if two objects are in thermal equilibrium with a third object (like a thermometer) then they are in thermal equilibrium with each other • Another way of saying it is that temperature is a measurable quantity and it tells us about the energy content of an object • this law asserts that we can define a temperature function, or more informally, that we can 'construct a thermometer'

  42. Thermal Equilibrium • if Q=0 then we are in “thermal equilibrium” • TA = TB Q A B

  43. Microscopic definition of T: ½ mv2 = 3/2 kB T v is average speed, kB is Boltzmann constant hot means faster motion What happens to the motion of molecules/atoms and absolute zero? Kelvin scale – 0 C = 273 K Thermal energy proportional to K, not C or F! http://jersey.uoregon.edu/vlab/Thermodynamics/therm1a.html

  44. The First Law of Thermodynamics – Energy Conservation Many statements: Energy is conserved Heat is a form of energy The energy of an isolated system (e.g. the universe) is constant Energy is conserved during any change in state. Specifically: Heat absorbed by a system + work done on the system = change in internal energy of the system Mathematically: Q+W=DU Q is heat, W is work and U is internal energy

  45. The 2nd Law of Thermodynamics Many formulations: It is impossible to convert heat completely into work. No perfect engine Can’t just pull heat out of the environment Heat cannot spontaneously flow from a material at lower temperature to a material at higher temperature. No perfect refrigerator In an isolated system, a process can occur only if it increases the total entropy of the system.

  46. Carnot Engine The Carnot Engine is an idealized engine that works in a reversible way What is a reversible engine? A refrigerator By adding work we can take heat from the cold reservoir and deposits it to the hot reservoir Again - 1st law works W+Q1 =Q2 Notice more heat is delivered than work done! Even a reversible engine is inefficient

  47. Carnot Efficiency The efficiency of a Carnot Engine T1 -T2)/T1 When does the efficiency approach 1? When T2=> 0 Example T1= 500oC = 773K T2= 0oC = 273K T1 -T2)/T1= 500/773= 65% This says W=65% Q2= 35% So if we take 100J from T1 we get 65J of work Redo if T1 is 100oC = 373k T1 -T2)/T1= 100/373= 26% so our 100J of energy only gives us 26J of work

  48. Efficiency First Law efficiency Work out/ energy in Second Law efficiency Work out/ Maximum possible work out using the same energy input Example - heating a house with electricity use resistive heating - first law efficiency = 100% - sounds good! use heat pump - can do much better (because we are using electricity to move energy from outside to inside) - first law efficiency > 200% !! Second law efficiency always less than 100% Tells you what the absolute best you can do is…

  49. U.S. Energy End Uses

  50. Peak Power Customers use 1000W hairdryers between 7 and 8 AM for 5 minutes. How much power should I plan for? 500 customers…

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