physics 171, physics and society review homework 1 due ... · physics 171, physics and society...

Physics 171, Physics and SocietyReview Homework 1

Due: 1pm Tues Sept 5th, 2017

Regular question

Remember, give justification for all your answers, and whenever the answer is anumber always show the units, e.g. “200 J”, “0.5 kg”.

1. A swimming pool is 20 feet long, 10 feet wide, and the water in it is on average 4feet deep.

(a) How many liters of water are there in the pool?

(b) How much energy, in Calories, is needed to heat one liter of water from 10◦

Centigrade (cold water from a faucet) to 30◦ Centigrade (swimming pooltemperature)?

(c) How much energy, in Calories, would it take to heat all the water in the poolfrom cold to swimming-pool temperature?

(d) How much is that in kiloWatt-hours (“kWh”)?

(e) How much (in dollars) would this much energy cost, if it was obtained byburning natural gas at a cost of 1¢ per kiloWatt-hour?

{14 points}

Multiple choice questions {2 points each}

For most questions there is one correct choice, but in some cases there may be morethan one, and to get full credit you must identify all the correct choices. In some casesnone of the choices may be correct. The grading scheme for multiple choice questionsis given on the course webpage.

1. The fact that energy is conserved means that(a) the total thermal energy of a system always stays the same(b) thermal energy cannot be converted into any other form of energy(c) energy is never created or destroyed(d) when energy changes form you always lose a significant fraction of it

2. Which of the following are units of energy?(a) Calorie (b) liter (c) kiloWatt (d) Watt-hour

3. NASCAR is thinking of reducing the allowed engine capacity for its racecars. Ifthey reduced it to 300 cubic inches, what would that be in liters (to 10% accuracy)?(a) 0.76 liters (b) 120 liters (c) 0.3 liters (d) 4.9 liters

4. One Watt-hour is the same as(a) 1000 Joules (b) 3600 Joules (c) 1 Joule (d) 3.6 Joules

5. Suppose you drive your car from the bottom of a hill to the top, and you stopthere. At that point, the chemical energy that was in the fuel has been turned into(a) kinetic energy of the car(b) gravitational potential energy of the car(c) nuclear energy in the atoms of the car(d) chemical energy in the body of the driver

6. When you burn natural gas to heat your house, the main process that is happeningis(a) thermal energy is being converted to electrical energy(b) electrical energy is being converted to thermal energy(c) electrical energy is being converted to chemical energy(d) chemical energy is being converted to thermal energy

7. When someone says “the energy density of gasoline is about 10 Calories per gram”,what they mean is(a) when a gram of gasoline is oxidized to carbon dioxide and water, it gives out10 Cal of energy(b) it takes 10 Cal of energy to extract a gram of gasoline from crude oil(c) when a gram of gasoline evaporates, it gives out 10 Cal of energy(d) in order for a gram of gasoline to evaporate, it must absorb 10 Cal of energy

8. The energy density of gasoline is about 10 Calories per gram. If a full gas tankcontains about 50 kg of gasoline, how much energy does it store?(a) 1.2 kWh (b) 12 kWh (c) 0.6 kWh (d) 600 kWh



Short report {20 points}Write a short critical summary (about 200 to 300 words) of a recent publishedarticle which is related to the topics covered so far in Chapter 1 of the textbook,namely energy storage, energy cost, etc. You can choose the article, but first readthe detailed instructions for writing the report which are on the course web page,http://physics.wustl.edu/alford/physoc/short_reports.html.

Your report should be printed on letter-size (8.5 by 11 inch) paper and stapled atthe end of the form for the multiple choice questions.


For most questions there is one correct choice, but in some cases there may be morethan one, and to get full credit you must identify all the correct choices. In some casesnone of the choices may be correct. The grading scheme for multiple choice questionsis given on the course webpage.

1. To within 20% accuracy, how much butter would have 1 kWh of chemical energy?(a) 20 g (b) half a pound (c) 120 g (d) an ounce

2. An iPad battery can store about 40 Watt-hours (Wh) of energy. When you plugit in to a wall socket to charge, it takes electricity which costs about 10¢ perkiloWatt-hour. What is the cost of the electricity needed to take the battery fromempty to fully charged?(a) $ 2.50 (b) 4 ¢ (c) 0.25 ¢ (d) 0.4 ¢

3. When you buy a gallon of gasoline, each kiloWatt-hour of the chemical energy youare buying costs roughly (to within 25%)(a) 10¢ (b) 3¢ (c) 95¢ (d) 360¢

4. Suppose you have a car that is powered only by lead-acid batteries. We want thecar to be able to go 75 miles on a full charge. To within 20% accuracy, how muchweight of batteries will the car need to contain?(a) 8000 lb (b) 4000 lb (c) 2000 lb (d) 6 lb

5. Which of the following is a major disadvantage of electric cars compared to gasolinecars?(a) batteries have a lower energy density than gasoline(b) batteries explode more readily than gasoline(c) electric motors are more efficient than gasoline engines(d) compared to buying a gallon of gasoline, it is much more expensive to buy theequivalent amount of electrical energy

http://physics.wustl.edu/alford/physoc/short_reports.html

6. In a hybrid car,(a) there is no gasoline tank(b) there is no gasoline engine(c) there is a fuel cell(d) there is a tank of Hydrogen

7. Which of the following is a feature of hybrid cars that helps them have better gasmileage than regular cars:(a) they use regenerative braking(b) they don’t have such good acceleration(c) they use a larger capacity engine(d) the battery pack is lighter than a filled fuel tank

8. Compared to gasoline, hydrogen has(a) lower energy density per unit volume and per unit mass(b) lower energy density per unit volume but higher energy density per unit mass(c) higher energy density per unit volume and per unit mass(d) higher energy density per unit volume but lower energy density per unit mass

9. In a Hydrogen-powered car, the role of the fuel cell is(a) converting chemical energy to electric energy(b) capturing the heat produced when hydrogen is burned(c) capturing carbon dioxide emitted by the engine(d) converting electric energy to kinetic energy of the car

10. Advantages of hydrogen-powered vehicles over gasoline-powered vehicles are:(a) one can use a variety of energy sources to create the hydrogen(b) hydrogen is not explosive when mixed with air(c) hydrogen fuel tanks will be smaller than gasoline tanks(d) we can mine naturally-available liquid hydrogen



Regular question

Remember, give justification for all your answers, and whenever the answer is anumber always show the units, e.g. “200 J”, “0.5 kg”.

1. The power produced by a person riding an exercise bicycle is about 0.15horsepower.

(a) How much is that in kiloWatts?

(b) How much work (in Calories) is done by the person in half an hour of riding?

(c) How many grams of chocolate chip cookies would you have to eat to providethat much energy? (Remember to include the efficiency factor: your body isnot 100% efficient at converting food to work.)

(d) Roughly how much would it cost to buy that much chocolate chip cookies ina supermarket, assuming the price is $2 for a packet of 8 cookies that weighabout 1 oz each?

(e) Suppose you used the exercise bicycle to power a light bulb (of the appropriateWattage) for half an hour. By how much is your electric bill reduced, throughusing human power instead of plugging the light bulb in to the electricitysupply?

{16 points}


For most questions there is one correct choice, but in some cases there may be morethan one, and to get full credit you must identify all the correct choices. In some casesnone of the choices may be correct: in that case choose answer (e). The grading schemefor multiple choice questions is given on the course webpage.

1. Suppose your electric bill for a whole year is $1200. If your electricity comes fromburning coal, how much coal (to 20% accuracy) was burned to supply you withelectricity for a year?(a) 600 kg (b) 3 tons (c) 6 tons (d) 13 tons

2. When a car crashes into a brick wall, what is a good estimate of the power of thecollision?(a) The kinetic energy of the car(b) The kinetic energy of the car divided by the amount of time for which the carhad been driving(c) The kinetic energy of the car divided by the mass of the car(d) The kinetic energy of the car divided by the duration of the collision

3. Which of the following sentences use the correct units?(Note: it doesn’t matter if the sentences are true or not, just whether they use theappropriate units)(a) A running person is developing about 1000 J of power.(b) A full tank of gasoline contains about 500 kJ of chemical energy(c) One horsepower is about 750 Watts/sec.(d) The power in sunlight is about 1 kW per square meter

4. If your body produces about 100 W in the form of heat, roughly (to within 20%)how much heat does your body produce in a day?(a) 2000 Cal (b) 8000 Cal (c) over a million Cal (d) 300 Cal

5. In a year, roughly (to within 20%) how much energy does the U.S. obtain fromwind?(a) 20 quads (b) 200 quads (c) 2 quads (d) 1018 J

6. Which of the following are true statements about U.S. energy use?(a) We get more energy from wind than from nuclear(b) We get more energy from coal than from renewables(c) We use more biomass energy than nuclear energy(d) We get more energy from solar than from wind

7. Which of the following are true statements about U.S. energy use?(a) Biomass is mostly used for generating electricity(b) Natural gas is mostly used for residential heating(c) Most of the electricity we generate comes from burning coal(d) More than half of the oil (petroleum) we use is for transportation



Short report {20 points}Write a short critical summary (about 200 to 300 words) of a recent published articlewhich is related to the topics covered so far in Chapter 1 and 2 of the textbook,namely power, temperature, heat, etc. You can choose the article, but first readthe detailed instructions for writing the report which are on the course web page,http://physics.wustl.edu/alford/physoc.



For most questions there is one correct choice, but in some cases there may be morethan one, and to get full credit you must identify all the correct choices. In some casesnone of the choices may be correct: choose (e). The grading scheme for multiple choicequestions is given on the course webpage.

1. If you run a 1kW hair dryer on its “high” setting for 1 minute, how much electricalenergy does it use, roughly (to within a factor of 2)?(a) 0.2 kWh (b) 0.02 kWh (c) 2.0 kWh (d) 20 kWh

2. An atom with A = 50 and Z = 24 has(a) 24 protons and 50 neutrons(b) 26 protons and 24 neutrons(c) 50 protons and 24 neutrons(d) 24 protons and 26 neutrons

3. Different isotopes of the same element have(a) the same number of protons in the nucleus(b) the same atomic mass number(c) the same number of neutrons in the nucleus(d) the same total number of neutrons plus protons

4. In air at room temperature(a) On average, the Oxygen molecules travel faster than the Nitrogen molecules(b) On average, the Nitrogen molecules travel faster than the Oxygen molecules(c) Oxygen and Nitrogen molecules have the same average velocity

5. Helium gas consists of Helium atoms, whereas Nitrogen gas consists of N2

molecules. In Helium gas at room temperature, the average velocity of a Heliumatom is (to within a factor of 2)(a) 1000 m s−1 (b) 4000 m s−1 (c) 3.5 × 106 m s−1 (d) 120 m s−1

http://physics.wustl.edu/alford/physoc

6. When you heat water from just above its freezing point to just below its boilingpoint, the kinetic energy of the molecules(a) increases by about 18%(b) increases by about 36%(c) doubles(d) it is impossible to say given this information

7. A piece of wood is at the same temperature as the air above it. This means thatthe molecules in the wood and in the air have the same(a) gravitational potential energy(b) number of electrons(c) average mass(d) average velocity

8. The heat energy in a lump of metal at room temperature is approximately thesame as(a) its kinetic energy if it were going at the speed of light(b) its chemical energy(c) its gravitational energy(d) its kinetic energy if it were going at the speed of sound

9. Cameron’s body consists, roughly speaking, of 80 kg of water at human bodytemperature (40 C). Suppose Cameron is standing next to a cold bath containing160 kg of water at room temperature (20 C). Which of the following are true?(a) The total heat energy of Cameron’s body is greater than the total heat energyof the water in the bath.(b) The total heat energy of Cameron’s body is the same as the total heat energyof the water in the bath.(c) The total heat energy of Cameron’s body is less than the total heat energy ofthe water in the bath.

10. The linear expansion coefficient of steel is about 10−5. A piece of railway line 500 mlong is laid down in the winter when the temperature is −5 C. By how much willthe length of the line increase when summer comes and the temperature reaches35 C?(a) 2 cm (b) 20 cm (c) 10 cm (d) 1 cm


Due: 1pm Tues Oct 3rd, 2017

Regular question

1. Researchers at MIT are working on a cell phone charger that is powered by theheat of the human body. Please see this article: http://tinyurl.com/ohudaoj.The idea is to use a “thermally regenerative electrochemical cycle” which is justa heat engine that turns the human body’s heat energy into electrical energy.

(a) What is the maximum possible efficiency of a portable heat engine that,when worn in regular indoor environments, converts human body heat toelectricity?

(b) The article says “Dr Chen believes it should be possible to convert heat toelectricity with around 12 per cent efficiency. . .”. How hot (in Centigrade)would a person’s body have to be for the cell phone charger to have anefficiency of 12% when converting body heat to electricity?

(c) Now we are going to estimate how much heat power flows into the charger sowe can estimate the electrical power it could produce. Roughly what is theheat power output of a human body at rest?

(d) Estimate the total surface area of the human body, assuming it canbe approximated as a cylinder of height 5 feet 6 inches and “waistline”(circumference) 30 inches You can ignore the top and bottom “endcaps” ofthe cylinder. Give your result in square centimeters.

(e) Using the results you have calculated above, estimate how much heat powercould be flowing into the charger, which is the size of a button.

(f) Using your answer to part (a), estimate how much electrical power could beproduced by the charger.

(g) A typical cell phone battery can hold about 5 Watt-hours of energy. Howlong would it take for the body-heat charger to supply that much energy tothe battery?

{20 points}



http://tinyurl.com/ohudaoj

1. Which contains more heat energy: one liter of water at room temperature, or twoliters of ice at 0 C?(a) there is more heat energy in the 1 liter of water(b) there is more heat energy in the two liters of ice(c) they have the same amount of heat energy(d) it is impossible to say given this information

2. A heat pump(a) extracts work from heat flowing out of a hot object(b) uses heat from a hot object to warm up a cold object(c) transfers heat from a cold object to a hot object(d) outputs an amount of heat that is equal to the work it takes as input

3. If a heat pump has a coefficient of performance equal to 3, then(a) for every 1 J of work going in, 3 J of heat come out(b) for every 3 J of work going in, 1 J of heat comes out(c) of the heat energy that comes out, most of it is coming from the work thatwent in(d) the hot region is losing heat energy at a rate of 3 W.

4. The mass of the nucleus is closest to(a) 99.9% of the mass of the whole atom(b) 10−5 of the mass of the whole atom(c) 10−15 of the mass of the whole atom(d) half the mass of the whole atom

5. The atomic mass of naturally-occurring Silicon is 28.09. From this you can deducethat(a) some Silicon atoms have more than 14 neutrons(b) some Silicon atoms have more than 14 protons(c) naturally-occurring Silicon contains impurities of other elements(d) a small fraction of Silicon atoms clump together to form molecules

6. A deuterium atom contains(a) 3 quarks and 1 electron (b) 6 quarks and 2 electrons(c) 9 quarks and 3 electrons (d) 6 quarks and 1 electron

7. Aluminum foil can stop(a) neutrons (b) alpha rays (c) beta rays (d) gamma rays

8. The isotope of Silver (Z = 47) with atomic mass number A = 111 (written 111Ag)is unstable and decays by β decay with a half life of about a week. What nucleusis produced in the decay of a 111Ag nucleus?(a) from this information one cannot predict it(b) some isotope of Rhodium (Rh)(c) some isotope of Palladium (Pd)(d) some isotope of Cadmium (Cd)


Due: 1pm Tues Oct 24th, 2017

Short report {20 points}Write a short critical summary (about 200 to 300 words) of a recent published articlewhich is related to the topics covered so far in Chapter 4 of the textbook, namelyradioactivity, its health effects, applications of radioactivity, etc. You can choose thearticle, but first read the detailed instructions for writing the report which are on thecourse web page, http://physics.wustl.edu/alford/physoc.




1. A terrorist wants to build a dirty bomb that, when it explodes, will cover a 50 m by100 m area with enough radioactive material so that a person in that area will geta dose of 20 mSv per hour. Before detonation, the bomb contains the radioactivematerial packed into a 1 m by 1 m area. Roughly what radiation dose will theunexploded bomb give to someone standing next to it?(a) 100 Sv/hour (b) 20 mSv/hour (c) 10 Sv/hour (d) 200 Sv/day

2. Potassium-Argon dating is useful for(a) measuring the age of early human bones(b) measuring the age of stone tools(c) measuring the age of ancient buildings(d) measuring the amount of Potassium in your body

3. If alcohol that is being sold for human consumption has no radioactivity in it, then(a) it was made from plants that died within the last few thousand years(b) it has been contaminated with biofuels(c) it has been filtered to ultra-high purity(d) it is illegal to sell it

4. 14C has a half-life of a few thousand years, so why is there any of it on earth?(a) it is created by beta decay of 14N(b) cosmic rays hit the 14C atoms and prevent them from decaying(c) it is created by cosmic rays hitting the atmosphere(d) it is constantly being created by biological processes

5. How was most of the Gold on earth originally created from other elements?(a) by a very skilled alchemist using the philosopher’s stone


(b) in the big bang, 14 billion years ago(c) in supernova explosions of massive stars(d) in collisions between neutron stars

6. How was most of the Oxygen on earth originally created from other elements?(a) by photosynthesis(b) in the big bang, 14 billion years ago(c) in supernova explosions of massive stars(d) in collisions between neutron stars

7. The half-life of 235U is 700 million years. A piece of very old rock now contains0.2 g of 235U. To 10% accuracy, how much 235U was there in the rock when it wasformed on earth 4 billion years ago?(a) 60 g (b) 6 g (c) 0.3 g (d) 10 g

8. Which of the following does not proceed by exponential growth?(a) human population in a resource-rich environment(b) the amount of gasoline in a car’s tank as it is being filled at a gas station(c) thickness of a piece of paper when it is repeatedly folded in half(d) amount of money in an account earning 2% compound interest

9. As long as you are alive, your body contains about 10−8 g of 14C. After you die,how long (to 10% accuracy) would it take until your corpse only contains 10−11 gof 14C?(a) 57,000 years (b) 40,000 years (c) 5700 years (d) 37,000 years

10. Suppose your money is in a bank account that earns compound interest at a rateof 1.5% per year. How long (to 10% accuracy) will it take for your savings todouble?(a) 5 years (b) 45 years (c) 70 years (d) 90 years


Due: 1pm Tues Oct 31, 2017

Regular question

1. Iodine-131 (13153I) is an unstable nucleus with a half life of 8 days. It decays by abeta decay followed by a gamma decay. It is used as a “tracer”, for example inmedicine and to detect leaks in buried pipes.

(a) In the beta decay of a 131I nucleus, what are the three decay products, notincluding “energy”? (For nuclei give their values of A and Z.)

(b) Suppose that a laboratory produced 100 g of 131I and sent it to you, but bythe time you receive the sample there is only 16 g left. How long ago (to thenearest day) was the sample produced?

(c) Estimate how many beta particles (electrons) are being produced per secondin your sample of 16 g of 131I.

(d) Another isotope of Iodine, 108I, decays by α decay with a half-life of 36 ms.What are the decay products (give A and Z for each nucleus produced)?

(e) Why would 108I be less suitable than 131I for detecting leaks in buried pipes?

{12 points}



1. The definition of “fissile” is: a material in which(a) the nuclei undergo fission when bombarded by neutrons(b) energy can be produced by both fission and fusion of the nuclei(c) a self-sustaining chain of fission events can occur(d) neutrons are slowed down by collisions with nuclei

2. Fission fragments tend to be highly radioactive because(a) they contain trace amounts of 235U(b) the heat released in the reaction deforms them into unstable shapes(c) they are large, unstable nuclei with more protons than a Uranium nucleus(d) the fission of Uranium produces unstable isotopes of smaller nuclei

3. Strontium-90 (90Sr) is(a) an example of a fission fragment(b) chemically similar to Carbon, and hence readily metabolized(c) dangerous because it takes thousands of years to decay(d) a dangerous component of nuclear fallout

4. A nuclear weapon, like the one dropped on Hiroshima, generates most of its energyby(a) fusion of 235U and 238U(b) fusion of hydrogen and helium(c) fission of 238U(d) fission of 235U

5. Typical nuclear power reactors in the U.S.A. use Uranium fuel that is(a) 3% 235U (b) 80% 235U (c) 0.7% 235U (d) pure 238U

6. A nuclear power plant produces electricity by(a) maintaining a beam of neutrons directed at a Uranium target(b) spinning Uranium in a centrifuge to generate a current in wires(c) heating steam and using it to drive turbines(d) using a heat pump to heat the Uranium and cause it to emit electrons

7. The role of the control rods in a nuclear reactor is(a) to absorb neutrons, which decreases the fission rate(b) to slow down the neutrons, which increases the fission rate(c) to slow down the neutrons, which decreases the fission rate(d) to emit neutrons, which increases the fission rate

8. In the Fukushima nuclear incident, the main cause of the meltdown was(a) cooling systems failed and heat was being generated by decaying fissionfragments(b) cooling systems failed and heat was being generated by fission of Uranium(c) the moderator leaked away(d) control rods failed and fission of Uranium got out of control


Due: 1pm Tues Nov 7th, 2017

Short report {20 points}Write a short critical summary (about 200 to 300 words) of a recent published articlewhich is related to the topics covered so far in Chapter 5 of the textbook, namelynuclear power, nuclear weapons, nuclear waste, etc. You can choose the article, but firstread the detailed instructions for writing the report which are on the course web page,http://physics.wustl.edu/alford/physoc.




1. A “fast breeder reactor” like the Integral Fast Reactor(a) makes its own fuel by converting 235U to Plutonium(b) makes its own fuel by converting 238U to fissile material(c) produces waste that is dangerously radioactive for more than ten thousandyears(d) produces waste that is not dangerously radioactive

2. In a Thorium reactor(a) 233U is converted to Thorium(b) Thorium is converted to 233U(c) Thorium is converted to Plutonium(d) 235U is converted to Plutonium

3. In a Molten Salt Thorium reactor(a) waste can be removed while the reactor is still running(b) there is no moderator(c) heat is produced by fission of 232Th(d) heat is produced by fusion of Thorium and Uranium

4. In a nuclear fusion reactor, the main source of energy is(a) Tritium nuclei combining with alpha particles(b) the breaking apart of Uranium nuclei into smaller pieces(c) Deuterium nuclei combining with Tritium nuclei(d) Tritium nuclei emitting beta rays to become Helium

5. It is difficult to make nuclei undergo fusion because(a) they tend to decay before there is time to fuse


(b) nuclei are so small(c) the electrons in the atoms cancel the positive charge of the nucleus(d) they repel each other electrostatically

6. We can estimate the amount of CO2 in the earth’s atmosphere hundreds ofthousands of years ago by(a) measuring 14C levels in tree rings in old trees(b) consulting written records of weather and agricultural activity(c) sampling air bubbles trapped in ancient ice(d) measuring abundances of isotopes of light elements in meteorites

7. During the last half million years,(a) every 100,000 years there has been an ice age lasting about 10,000 years(b) there has been only one ice age and it lasted about 100,000 years(c) there has been only one ice age and it lasted about 10,000 years(d) most of the time the earth has been in ice ages

8. The average global temperature during the decade 2000-2010 was(a) higher than during any decade since 1900(b) higher than at any time since the first century C.E.(c) higher than at any time since the dawn of civilization (around 6000 B.C.E.)(d) higher than at any time since the last ice age

9. During the last 100 years, global average sea level(a) has fluctuated around a roughly constant value(b) has risen more than 10 cm(c) rose at first and is now falling again(d) has fallen between 5 and 10 cm

10. Compared to today, average global temperature during the last ice age was onaverage about(a) 10 C cooler (b) 2 C cooler (c) the same as today (d) 6 C cooler(there is one correct answer to this question)


Due: 1pm, Tues Nov 14th, 2017

Regular question

1. For the planet Mars, the power per unit area in sunlight is F = 590 Wm−2; theabsorption fraction for sunlight is α = 0.75 and the emissivity for infrared radiationis ε = 0.93.

(a) Estimate the surface temperature of Mars, in Kelvin, Centigrade, andFahrenheit.

(b) Compare your estimate to the average surface temperature of Earth. Whatis the main reason for the difference?

(c) Suppose that we wanted to prepare Mars for human settlement (this is called“terraforming”) by modifying its emissivity; for example, by releasing CO2

that is trapped in the Martian polar ice caps. What value of the emissivityshould we aim for, such that the average surface temperature of Mars wouldbe the same as Earth’s?

{10 points}



1. The term “greenhouse effect” refers to(a) scattering of sunlight by particles in the atmosphere(b) warming of earth due to gases in the atmosphere that are not transparent toinfrared light(c) storage of heat in clouds(d) emission of visible light from the earth’s surface

2. The earth absorbs heat from sunlight. It loses significant amounts of heat to spacevia(a) convection in the atmosphere(b) emission of infra-red light(c) emission of visible light(d) convection in the oceans

3. Which of the following is/are greenhouse gases(a) oxygen (O2) (b) argon (c) carbon dioxide (d) nitrogen

4. Carbon dioxide levels in the atmosphere have changed over the last 100 years byabout(a) 0.6% increase (b) 36% increase (c) 6% increase (d) 6% decrease

5. Over the last 30 years, we have seen(a) an increase in the number of hurricanes per year that hit the U.S. mainland(b) an increase in the number of tornadoes per year(c) an increase in the area of the Arctic ice cap(d) an increase in the area of permafrost in Alaska

6. Since 1980, the area of Arctic sea ice cover has (to within a few percent)(a) halved (b) increased by less than 5%(c) decreased by 10 to 20% (d) decreased by over 20%

7. Which of the following are examples of a positive feedback loop for global warming?(a) increased temperature means plants grow faster and absorb more CO2

(b) increasing temperature means more evaporation, so more white clouds(c) increasing temperature means permafrost melts and releases methane(d) increasing temperature means ice caps melt, revealing darker surfaces

8. Between 2002 and 2010, the average annual income of people in Kenya doubled.One would expect that during this time the annual energy consumption per personin Kenya(a) went down by 50%(b) changed by less than 10%(c) quadrupled(d) doubled

9. According to the histogram shown in class, from 2012 to 2040 total world energyconsumption is expected to change by(a) a factor of 2 increase(b) 40-50% increase(c) 0-10% increase(d) 0-10% decrease

10. According to the histogram shown in class, which country has the largest naturalreserves of coal?(a) U.S. (b) Russia (c) China (d) India


Due: 1pm, Tues Nov 21, 2017

Short report {20 points}

Write a short critical summary (about 200 to 300 words) of a recent publishedarticle which is related to the topic of climate change, or greenhouse gas reduction,or alternate energy technologies. You can choose the article, but first read thedetailed instructions for writing the report which are on the course web page, http://physics.wustl.edu/alford/physoc.

Multiple choice questions {2 points each}For most questions there is one correct choice, but in some cases there may be morethan one, and to get full credit you must identify all the correct choices. In some casesnone of the choices may be correct: choose (e). The grading scheme for multiple choicequestions is given on the course webpage.

1. Hydraulic fracturing (“fracking”) uses water and sand to(a) drill deeper than was previously possible(b) create synthetic oil from coal(c) deposit carbon dioxide in underground shale vaults(d) extract oil or gas from rock

2. In terms of GHG emitted per passenger per mile traveled,(a) conventional cars are better (lower emission) than aircraft(b) a mostly empty (“off peak”) bus is better than light rail(c) a full (“peak”) bus is better than light rail(d) large aircraft are worse than small aircraft

3. Carbon “Cap and Trade” means that if a country emits more CO2 than its allowedmaximum then(a) it will suffer trade sanctions(b) it will have its cap increased(c) it has to buy carbon credits(d) it will suffer trade sanctions

4. Which of the following countries met their Kyoto treaty targets?(a) United States (b) Australia (c) Canada (d) Greece

5. Water vapor is a greenhouse gas. So why don’t we count emissions of water vaporfrom cars, power plants, etc, as GHG emissions?(a) the GHG effects are cancelled by the formation of clouds that reflect sunlight(b) water vapor has a short lifetime: any extra water vapor we add to theatmosphere quickly condenses out(c) water vapor naturally transforms into CO2

(d) global warming means that there is less water vapor in the atmosphere



6. Which of the following are examples of conservation as a way of reducing energyconsumption?(a) using better insulation in buildings(b) putting a tax on fossil fuels(c) finding more efficient energy storage mechanisms(d) planting trees to reduce atmospheric CO2 levels.

7. Wind turbines(a) provide more power than solar power in U.S. annual energy consumption(b) provide “on demand” power(c) are a major source of greenhouse gases(d) provide more power than nuclear power stations in U.S. annual energyconsumption

8. Hydroelectric power stations(a) only provide power intermittently(b) are inefficient because water has to be pumped into the reservoir(c) can provide power near any large population center(d) convert gravitational potential energy into electrical energy

9. Geothermal electricity(a) produces as much GHG emission as natural gas(b) uses heat pumps to transfer earth’s heat to buildings(c) uses heat from earth’s interior to make steam to drive turbines(d) turns gravitational potential energy of water into electrical energy

10. Significant advantages of nuclear power include(a) there are no harmful waste products(b) the fuel is abundant and costs nothing(c) power plants are potential targets for terrorists(d) power production does not emit greenhouse gases


Due: 1pm, Tues Nov 24th, 2017

1. In this question, use c = 3.00 × 108m/s and h = 4.13 × 10−15 eV s.

(a) A beam of light contains photons of wavelength 486 nm. What color of lightis it?

(b) What is the energy, in electron volts (eV) of each photon in the beam? Givean answer with 3 digits of accuracy.

(c) Could the light have come from excited Hydrogen atoms? If so, whattransition (give the initial and final values of n for the electron) would givelight of this wavelength?

(d) The power in the beam is 10 mW (same as a very bright laser pointer). Howmany photons per second is the beam delivering?

(e) Another beam delivers the same amount of power, but the light is red. Doesthe second beam deliver more photons per second or less photons per second?Explain your answer.

{10 points}



1. Photosynthesis is(a) the conversion of plant materials to coal, oil, or natural gas(b) a process in plants which is the same as respiration in animals(c) a process by which plants make sugars from CO2 in the air(d) a process by which sugars are burned to release CO2

2. Advantages of biofuels over fossil fuels include(a) biofuels produce more energy per gram of fuel(b) biofuels burn more readily(c) burning of biofuels does not increase atmospheric GHG levels(d) fossil fuels do not derive from living material

3. In “classical” (non-quantum-mechanical) physics,(a) things are either a wave or a particle(b) some things are both waves and particles(c) everything is waves(d) everything is particles

4. According to classical physics,(a) atoms have discrete energy levels (b) atoms collapse in less than a second(c) atoms eventually collapse after billions of years (d) atoms are stable

5. According to quantum mechanics,(a) everything is made of waves(b) everything is made of particles described by wavefunctions(c) energy is not conserved(d) particles have definite positions, but their speed is uncertain

6. In quantum mechanics, an electron bound in an atom(a) has a negative energy (b) has only a finite number of possible energies(c) has an infinite number of possible energies (d) can have any positive energy

7. Which of the following is a reasonably accurate sketch of the wavefunction of anelectron in the second excited state of Hydrogen?ψ

r

ψ

r

ψ

r

(a) (b) (c) (d)

ψ

r

8. If a photon of energy 5 eV meets a Hydrogen atom in its ground state,(a) the photon can be absorbed, and the electron will then move up to to a higher-energy bound state(b) the photon can be absorbed, and the electron will then be ejected from theatom(c) the photon cannot be absorbed(d) the electron will stay in the same energy state but oscillate at a higherfrequency

9. A pulse of laser light is produced by(a) a large number of atoms all emitting photons simultaneously(b) a chain reaction as one atom emitting a photon stimulates other atoms to dothe same(c) a large number of atoms all absorbing photons of the same frequency(d) each photon producing an additional photon when it reflects off the end mirrors

10. A laser is useful because(a) it does not need any power to be supplied to it(b) its light contains photons of many different energies(c) it emits electrons as well as light(d) its light can be very intense

physics 171, physics and society review homework 1 due ... · physics 171, physics and society...

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