Physics and Society. Prof. Mark Alford. Fall 2018

Transcription

1 Physics and Society Prof. Mark Alford Fall 2018

2 Exponential notation 3,000,000 = = = = = 10 3 = = = = = = millionths =

3 Metric prefixes G giga billion GW = 10 9 W 1 giga-watt = a billion Watts M mega million 1,000,000 = MT = 10 6 T 1 mega-tonne = a million Tonnes k kilo thousand 1,000 = kg = 1000 g c centi hundredth 0.01 = = cm = 0.01 m m milli thousandth = = mm = m µ micro millionth 1 1,000,000 = µm = 10 6 m n nano billionth nm = 10 9 m

4 Energy, meaning... Nice, but... our goal is to understand this,

5 and this:

6 Energy as Money Energy is like Money. The amount of energy you have available determines what you can get done. Energy and Money are both conserved: they can be transferred between different places and take different forms, but the total amount is unchanged. Except that governments can print money. How do we obtain energy from our environment? Coal, Oil, Sunlight... How do we store energy for future use? Gasoline, Batteries, Food... How do we transport energy? Electric power lines, Oil tankers... How do we use energy to get things done? Engines, Motors, Muscles, Light bulbs, Speakers...

7 Energy Topics Forms of energy Kinetic, Chemical, Nuclear, Electrical, Thermal Quantifying amounts of energy Units: Calories, kilowatt-hours, etc Storing energy Batteries, Food, Fuels, Uranium... Which is best? Application: comparison of electric cars, hybrid cars, and regular cars Cost of energy Coal vs Electricity, Gas, Oil, etc Kinetic energy bullets, asteroids, flywheels Power: rate of flow of energy

8 Forms of energy Energy is taken in or given out during a change of state Energy that a car has when it is driving at 50 mi/hr (moving stationary) Energy stored in TNT, released when it explodes (TNT hot gas of Nitrogen, water, etc) (Kinetic Energy) (Chemical Energy) Energy stored in a gram of butter, released when it is burned (fat water and CO 2 ) (Chemical Energy) Energy that a brick has when at the top of a building (high up low down) (Gravitational Potential Energy) Energy stored in a Uranium nucleus, released when it decays (Uranium two smaller nuclei) (Nuclear Energy) Energy stored in wires that are carrying an electric current (current flowing no current flowing) (Electrical Energy) Energy stored as heat, released when hot object cools (hotter cooler) (Thermal Energy)

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10 Energy Storage We have two requirements which sometimes conflict: Accessibility: energy can easily be extracted from container and used. High energy density: lots of energy stored per gram of container.

11 Hybrid Cars A hybrid car is a gasoline powered car that achieves higher fuel efficiency. The engine is just big enough to run the car at normal speed. For acceleration, the battery supplies the extra power. Small gasoline engine and rechargeable battery Engine runs at max efficiency at a constant rate Engine runs a generator to make electricity Electric motor drives wheels (In a parallel hybrid, engine may also drive wheels) Regenerative braking recharges battery

12 Types of Hybrid Car

13 Operation of Hybrid Car

14 Hydrogen Fuel Cell Fuel cell burns Hydrogen to make electricity. So we can use Hydrogen as a fuel, i.e. a way to store and transport energy.

15 Actual Hydrogen fuel cell

16 Hydrogen fuel cell car

17 Methanol Fuel Cell Anode: CH 3 OH + H 2 O 6 H + + 6e + CO 2

18 Methanol Fuel Cell Car

19 Marginal Cost of Energy Fuel Marginal Cost = cost per kwh once generator is in place Market cost Cost per kwh of heat Wholesale Fuels: Coal $60/ton Natural gas $3 per 10 3 cubic feet Oil $70 per barrel Retail Fuels: Natural Gas $10 per 10 3 cubic feet 3 Gasoline $2.80 per gallon 10 Electricity $0.10 per kwh Cost per kwh when converted to electricity (This table uses more recent prices than the table in the book.)

20 Levelized Cost of Energy (LCOE) For electricity generation, covering whole lifetime of the generator: construction, operation, decommissioning (total amount spent) LCOE = Average Cost = (total energy generated)

21 Key to LCOE table PV means photovoltaic : regular solar panels that convert sunlight directly to electricity. C&I means commercial and industrial IGCC means Integrated Gasification Combined Cycle : a more efficient way to use coal, converting it to gas ( syngas ) and burning that. A microturbine is a smaller generator that combines all the components (compressor, combustor, turbine and electric generator) on a single shaft or two. It s not clear what fuel is envisaged is this table. gas peaking means a natural gas burning power plant that runs only when there is a high demand. gas combined cycle means a natural gas power plant that uses a series of heat engines to maximize efficiency.

22 Kinetic energy: Cretaceous asteroid impact 65 million years ago, near present-day Yukutan, Mexico Diameter: 10 miles; speed: 20 miles/sec Impact crater: 60 miles across, 20 miles deep Energy released: 100 million megatons of TNT (10 14 tons) Impact site heated to over 1 million Centigrade Asteroid, rock, etc instantly vaporized Worldwide climate change, extinction of dinosaurs, etc Why such a large explosion? (No explosives involved!) Kinetic Energy Thermal Energy

23 Examples of power consumption

24 History of world energy generation

25 U.S. annual energy consumption over time

26 U.S. annual energy consumption

27 U.S. annual energy consumption and use

28 Atoms and Heat Cretaceous asteroid impact: all its kinetic energy was turned to Heat. Why? How does KE turn to heat? What is heat? Why did this make an explosion? Scientists predict that global warming could cause sea levels to rise by several feet, even if no ice melts. Why? If you run a refrigerator with the door open, will the room get colder or warmer? Burning fuel to provide heat is almost 100% efficient. But there are heating methods that are more than 100% efficient, such as heat pumps. How do they work?

29 1 1 2 H Li Na Be 12 Mg K Ca Rb Sr Cs Ba La Fr (223) Ra (226) Periodic Table of the Elements 21 Sc Y Ac (227) 22 Ti Zr Hf Rf (261) 23 V Nb Ta Db (262) 24 Cr Mo W Sg (263) 25 Mn Tc (98) 75 Re Bh 26 Fe Ru Os Hs 27 Co Rh Ir Mt 28 Ni Pd Pt Cu Ag Au (262) (265) (266) (269) (272) 30 Zn Cd Hg (277) H He B C N O F Ne Al Ga In Tl Si Ge Sn Pb (289) (287) P As Sb Bi S Se Te Po (209) 116 (289) Cl Br Ar 36 Kr 53 I At (210) Xe Rn (222) 118 (293) Ce Pr Nd Pm (145) 62 Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Pa U Np (237) 94 Pu (244) 95 Am (243) 96 Cm (247) 97 Bk (247) 98 Cf (251) 99 Es (252) 100 Fm (257) 101 Md (258) 102 No (259) 103 Lr (262) S.E. Van Bramer, 7/22/ IUPAC masses and Approved Names from masses for from C&EN, March 13, 1995, P from from C&EN July 19, and 118 from

30 Atom and nucleus Atom electron Nucleus m proton neutron m

31 Thermal Expansion: railroads Expansion joints Without expansion joints

32 Thermal Expansion: bridges Bridge expansion joint

33 Thermal Expansion

34 Heat flow with no heat engine or pump Suppose you have a hot region next to a cold region. Heat will flow from one to the other. Hot region P hot P cold Cold Region T hot T cold P hot Joules/sec are leaving the hot region, and P cold Joules/sec are flowing into the cold region So by conservation of energy P hot = P cold A heat engine siphons off some of that heat flow as useful work. A heat pump does work and reverses the heat flow.

35 Heat engine A heat engine siphons off some of the heat flow as useful work. Hot region Heat Cold Region P Engine P cold hot T hot T cold W By conservation of energy, P hot = P cold + W Efficiency = fraction of the available heat that is converted to work = W P hot. Efficiency is limited by the 2nd law of thermodynamics, W P hot T hot T cold T hot NB: Temperatures must be expressed in Kelvin!

36 Heat Pump A heat pump does work to make heat flow the wrong way, from cold to hot. Hot region Heat Cold Region P Pump P cold hot T hot T cold W By conservation of energy, P hot = P cold + W Coeff. of Performance, CoP = amount of heat produced per amount of work done CoP is limited by the 2nd law of thermodynamics, = P hot W. P hot W T hot T hot T cold

37 Nuclei and radioactivity You are radioactive, although you get less radioactive after you die. The bureau of alcohol, tobacco, and firearms tests wine and spirits for radioactivity. If they aren t radioactive enough, they can t be sold to the public. What percentage of deaths from the Hiroshima atomic bomb were due to radiation-induced cancer? About 2%. Biofuels (e.g. ethanol from corn or sugar cane) are radioactive. Fossil fuels are not.

38 Types of radiation

39 The spectrum of electromagnetic radiation c = f λ

40 Radiation damage scale Radiation damage to living tissue is measured in Sievert. Older unit was rem: 100 rem = 1 Sievert; 1 rem = 10 msv 1 Sv (whole-body) is the damage from 200 billion gamma rays going through each cm 3 of your body. Short-term effects: radiation sickness (only from high doses) Long-term effects: increased cancer risk

41 Short term: radiation sickness Whole-body acute dose Resulting radiation sickness < 1 Sv does not cause short-term illness 1-2 Sv nausea, loss of hair, rarely fatal if treated 3-5 Sv 50% chance of death in 60 days (if untreated) > 10 Sv incapacitated within 1-2 hours, probable death So LD50 for radiation is 3 Sv to 5 Sv full-body acute dose. ( acute means all at once )

42 Long term: increased cancer risk extra risk = dose/(25 Sv) Activity Associated whole-body ( effective ) radiation dose Background radiation 0.35 µsv/hr cancer prob (cosmic rays, rocks, etc) 0.01 msv/day 3 msv/yr /yr Denver background 4 msv/yr /yr 1 Dental X-ray msv Intercontinental flight 0.03 msv Mammogram 0.4 msv Full-body CT scan 20 msv Maximum expected for neighbors of Fukushima reactor in msv (All approximate, to within a factor of about 2.) For more examples see

43 Cancer risk from low-level radiation Japanese atomic bomb survivor data National Academy Study of Radiation Health Risks, Sv = 100 rem

44 Origin of elements Many elements are produced in supernovas ( exploding stars ) and neutron star mergers.

45 Heavy star: Life cycle of stars Light stars, like our sun, don t explode, but become brown dwarf stars.

46 Remnants of a supernova The dust cloud around a supernova is rich in medium-mass elements. (Crab nebula, A.D. 1054)

47 Neutron star collisions On Mon Oct 16, 2017, the LIGO collaboration announced that it has detected gravitational waves from two colliding neutron stars. Computer simulations show that such collisions produce lots of heavy elements.