Past Exams and Solution Hints

Physics 1070 First Hourly Exam October 14, 1998

This is a closed book exam. Be careful not to share your answers to this exam with anyone else, since the hallmark of science is honesty and integrity. Write all your answers carefully, completely, concisely, and legibly in the spaces provided on these exam sheets. Anything that can't be easily read and understood by the grader will be marked wrong, The 100 points for this exam will be worth 15% of your final grade.

1. Matching: Choose the item in the first column that, on the basis of course readins and discussions, most closely associates with the description in the second. (30 points: 3 for each correct item). [Bonus: extra 5 points - Define, in one or two sentences, any one of the items listed in the right hand column.]

10 a) the desire "to understand communally"

15 b) methods "that successfully modify and control man's environment"

1 c) useful but incomplete picture of the real physical world

11 d) displacement of an object times the component of force in the direction of that displacement

9 e) batteries produce electrical energy

16 f) the product of wave frequency and wavelength

3 g) while rising, an object, whose total mechanical energy constant, loses kinetic energy

5 h) the average of the mean kinetic energies of the random part of molecular motion

6 i) equal amounts of water and alcohol, subject to the input of equal amounts of heat energy, undergo

different temperature changes

2 j) the ability to do work in virtue of motion

1) model

2) kinetic energy

3) potential energy

4) religion

5) temperature

6) heat capacity

7) heat energy

8) magic

9) chemical energy

10) science

11) work

12) nuclear energy

13) wave energy

14) wave amplitude

15) technology

16) wave velocity

17) electric fields

18) magnetic fields

19) electromagnetic

fields

20) neutrinos

2. Mark the following statements either true (T) or false (F) on the basis of the reading and discussions of this class. (30 points, 3 for each correct item).

F a) In the present day world, more automobiles are built than bicycles.

T b) Currently, more poultry than beef is produced and consumed worldwide.

T c) Currently, worldwide, the percentage of illiterate women is dropping rapidly.

F d) Currently, access to adequate sanitation facilities is increasing worldwide.

T e) While cigarette consumption is decreasing in the world's industrial countries, it is increasing in the "developing" nations.

T f) Though world population is still increasing, the rate of its growth has begun to drop

F g) With the introduction of new drugs, the rate of HIV infection is now dropping worldwide.

F h) During the last century, the average temperature of the earth's surface has decreased as the carbon dioxide concentration in the atmosphere has increased.

F i) Two clay balls collide with each other and stick together; the total random kinetic

energy of all of the clay molecules is the same after the collision as it was before.

F j) More energy input is required to heat one kg of water from 0 'C to 100 'C than is required to turn the water at 100 'C into steam.

3. Multiple choice: Pick the numbered items which best completes the statement (20 points, 4 for each correct item).

1 a) The energy given off when 0.5 kg of water is cooled from 95'C to 25'C is

1. 70 calories

2. 35 calories

3. Not enough information given to determine an answer.

4. No energy is given off since energy conserved.

5. None of these is correct.

4 b) It is more efficient to cool a cup of hot water by adding ice cubes rather than adding an equal amount of cold water because

1 . The ice is colder than the cold water.

2. The ice will dilute the drink less than the water.

3. Ice has a greater heat capacity than water.

4. Ice undergoes a change of state.

5. None of these statements is correct.

3. c) Electromagnetic waves and matter differ in that

1 . Only matter can transfer energy from place to place.

2. Only electromagnetic waves can exert force on material objects.

3. Only matter can carry ordinary mass from place to place.

4. All of the above completions are correct.

5. None of these completions is correct.

3 or 4 d) In a nuclear reaction

1. Total energy is not conserved.

2. Total electric charge is not conserved.

3. The number of nucleons does not change.

4. The number of protons may change.

5. None of the above statements is correct.

2 e) A battery converts 1000 joules of chemical energy into electrical energy. The resultant electric current is used to drive an electric motor which lifts a 2kg mass. If the combined battery-motor system is 80% efficient, the mass can be lifted through a height of "7

1. 50 meters

2. 40 meters 80% x 1000 = 800 = mgh = 2x10xh.

3. 1 meter

4. Not enough information given to obtain an answer. h = 800/20 = 40m.

5. None of the above.

4. Short essays: Answer any two of the following questions (20 points, 10 for each correct essay).

a) Use Occam's Razor to rule out Velikovsky's explanation of biblical events.

b) How does the molecular theory of matter account for the loss of mechanical energy due to friction?

c) Describe the chain of energy conversions, as far back to the beginning as you can, which leads to you hearing the morning news on your home radio.

d) List and describe the similarities and differences between sound waves and electromagnetic waves.

e) Describe the similarities and differences between magical, religious, and scientific approaches to a physical problem. Include in your discussion the relative benefits and deficiencies of the different approaches.

points to be mad,e and elaborated upon, in these short essays:

a) Fewest possible hypotheses, consistency with overall picture. Velikovsky requires contradicting standard science. Biblical stories can be accounted for in other ways.

b)Friction occurs at the rubbing together of two materials implying molecules of one bump into molecules of other. Hence, overall K.E. of motion transformed int K.E. of molecules implying increased temperature.

c)Chemical energy of fuel (coal, oil,...) becomes K.E. of dynamo, becomes electrical energy, transmitted to home radio as well as transmitter. Sound energy from announcer becomes electrical energy in microphone, modifies electrical energy in transmitting antenna, becomes electromagnetic wave energy, travels to your receiver, modifies electrical energy in your home radio, produces sound energy in your loudspeaker, sound travels to ear, produces mechanical vibrating energy oif your eardrum, produces electrical and chemical energy changes in your nervous system, goes to brain, is recognized there.

d) Similarities: both are wave, characterized by amplitude, frequency, wavelength, speed, wave properties such as diffraction, refraction, reflection, interference.

Differences; sound is longitudinal wave, em is transverse; sound is material disturbance, em is in vacuum ( so sound won't travel thru vacuum, em will); sound speed determined by specific material thru which it passes, em speed universal; em speed much greater than sound speed; sound produced by mechanical vibration, em wave produced by oscillating electric charges; sound detected by producing mechanical vibrations; em detected by producing oscillations of electric charges in matter.

e) Similarities: all observe the phenomenon, all attempt to "explain" it and to control ot for human benefit.

Differences: Religion -effect due to "supreme being" who can be petitioned to control phenomenon

Magic - Rites, incantations, known only to a select few, can "force" nature or "supreme being" ("god") to control phenomenon to benefit of magician (=select few)

Science: - understand phenomenon within general body ofscientific law, may. use effects own properties to gain beneficial use of it; cannot force anything against laws.

Magic and Religion have numerous pschological and social advantages but they usually don't work whereas science often does.

Physics 1070 Second Hourly Exam November 23, 1998

This is a closed book hourly exam. Anything that can't be easily read and understood by the grader will be marked wrong. The 100 points for this exam will be worth 15% of your final grade.

Useful Information:

1 Calorie = 4184 joules

OoC = 273K

Second Law efficiency = I - Tf /Ti

1.Matching: Choose the item in the first column that, on the basis of course readings and discussions, most closely associates with the description in the second. (30 points: 3 for each correct item.) [Bonus: extra 10 points - define, in one or two sentences, any two of

these items listed in the second column.]

f)

9 a) The spread through a given aperature increases with increasing wavelength.

1b) The total electromagnetic radiation given off by an ideal hot body increases with the fourth power of the absolute temperature.

11 c) Fusion of four hydrogen atoms to produce one helium atom, positrons, neutrinos, and energy.

20 d) Some of the solar radiation incident upon the earth's atmosphere is reflected back into space

without change.

6 e)Some of the solar energy incident upon the earth is absorbed, reradiated at the earth's characteristic temperature, and partially trapped.

4 f) combining water, carbon dioxide, and radiant energy to produce carbohydrates and oxygen.

10 g) absorbing a photon in a p-n junction.

7 h) uranium - 238

12 i) Total energy in a system can only be increased if energy is brought in from outside of the system.

14 j) Heat energy can be lost from a system even if the system is completely surrounded by a vacuum.

1 . Stefan-Boltzman Law

2. critical mass

3. respiration

4. photosynthesis

5. fissile material

6. greenhouse effect

7. fertile material

8. nuclear binding energy

9. diffraction

10. particle-hole pair

11. solar energy source

12. 1" Law of Thermodynamic

13. 2nd Law of Thermodynamic

14. radiation

15. conduction

16. convection

17. entropy

18. n-type semiconductor

19. p-type semiconductor

20. albedo

True or False: mark the following statements either true (T) or false (F) on the basis of the class readings and discussions. (30 points, 3 points for each correct item.) [Bonus: 10 points - explain in 2 or 3 sentences, why any two of these statements are true or false.]

a) The amount of fish consumed per person in the world population continues to increase greatly. F

b) World grain stocks have become increasingly secure. F

c) Since Russian soil is not as productive as that of the U.S., Russian agriculture uses more fertilizer than does the U.S. -F

d) The use of solar energy is not gaining because of the increasing cost of solar cells. -F

e) Wind power supplies more energy to the world than do solar cells.-T

f) Wworld reliance upon nuclear power has recently begun to rapidly increase. -F

g) World forest area has begun to increase because of the recognized need for carbon

sequestration. -FI

h) World energy consumption exceeds the energy available from a high-proteinanimal cycle agriculture. -T

i) A breeder reactor makes efficient use of neutrons to turn fertile materials into fissile materials.T

3. Multiple choice: Pick the numbered items which best completes the statement (20 Roints, 4 for each correct item.) [Bonus: 5 points - in 2 or 3 sentences, explain any one of your answers.]

2 a ) Assume that the air temperature is 27'C and that the temperature of the hot steam entering a steam turbine is 327'C. The maximum possible efficiency of this turbine is

1. 100%

2. 50% efficiency = 1 - Tf / Ti = 1 (273+27)/(273+327) = 1 - 300/600 =1/2 = 50%

3. 0%

4. None of the above is corTect.

5. Not enough information is given to obtain an answer.

5 b) You only have electricity available to heat your home. For a given constant room temperature, your electric bill would be lowest if you

1. Heated directly with electric baseboard heating.

2. Used the electricity to run a heat pump whose evaporator were in the air outside of the house.

3. Used the electricity to run a beat pump whose evaporator were in the air inside of the house.

4. Used the electricity to heat water for a radiator system.

5. Used the electricity to run a heat pump whose evaporator was deep in the earth below your house.

3 c) As the temperature inside a chamber increases from -73'C to + 127'C, the average kinetic energy of the random motion of the molecules in the chamber

1. remains the same -73o = 200K

2. increases by the ratio 127/ 73 127o = 400K

3. doubles

4. decreases by the ratio 73/127 400/200 = 2

5. None of the above is correct.

4 d) In a normally operating nuclear reactor, "poisons" are

1. radioactive materials dangerous to reactor operators.

2. radioactive materials spread to the surrounding countryside.

3. materials which convert fissile nuclei to fertile nuclei.

4. fission products which absorb neutrons without contributing to the chain reaction fission process.

5. None of the above are correct explanations

5 e)In contrast to single glazing (single ordinary sheet of glass), double glazed windows consists of two parallel sheets of ordinary glass separated by a vacuum. When replacing my single glazed windows with double glazed, I

1. reduce heat lost by radiation

2. reduce heat lost by conduction

3. reduce heat lost by convection

4. both (1) and (2)

5. both (2) and (3)

6. both (1) and (3)

7. (1), (2), and (3)

8. None of the above are correct.


Short essays: Answer any two of the following. questions (20 points, 10 for each correct essay.)

a) Why are chimneys required for a furnace heating a home with fossil fuels whereas they are not required for electric heating? In what ways is electric heating more efficient than furnace heating, in what ways is it less efficient?

Fossil fuels provide heat via combustion; waste products of combustion must be taken out of house and fresh oxygen drawn in from outside. Chimney vents waste gases and provides draft for new oxygen.

Electric power comes from central station -either fossil, nuclear, wind, or water powered. If combustion occurs, it occurs at central station, not at home.

Electric heating can occur right where needed - doesn't have to be transported from furnace to place of need.

But lot of electrical energy lost on way from powerplant to place of need.

b) Why, under present U.S. circumstances, is it inadvisable to raise additional corn just for conversion into fuel energy?

We use lot of fossil fuels - fertilyzer, farm machines, food processing - to grow and utilyze the corn. Does not appear wise to use up fuel to, produce fuel.

If we could tap all of the solar energy captured in the corn without using fossil fuels, then corn would be a useful supply of fuel.

c) In order ro run an irreversible process backward, one must supply it with energy from outside. No such energy is required to reverse a reversible process. Why? What sort of entropy changes are associated with each process?

Running irreversible process backwards means decreasing the entropy of the system. According to the Second Law, entropy can only be decreased if energy is put into the system. Reversible processes do not imply decrease of entropy, hence require no energy input.

Reversible process does not involve heat.

Irreversible processes often implies evolution of heat. To run it backwards, you must put heat back in.

d)Suppose the chemical energy contained in coal is 5000 calories/kilogram. The materials in a homemade steam engine cannot withstand temperatures higher than 500oC. What is the maximum available amount of useful work that can be gotten out of ten kilograms of coal when using the engine? How much unavailable heat will there be? What happens to this unavailable heat?

Go from 500 o =773K to room temperature = 20o =293K. The efficiency = 1 - 293/773

=1 -.38 = .62 = 62%

Input energy = 5000 cal/kg x 10 kg = 50,000cCal

Useful work = efficiency x input energy = 62% x 50,000 = 31,000.

Unavailable energy is what's left over =50, 000 - 31,000 = 19, 000 cal which goes to heat up the surroundings.

e) Argue for or against a policy of relying upon breeder reactors to supply the U.S. with its requirements for electrical energy.

For; 1) Use up the energy contained in all of the earth's uranium rather than just that in the 0.7%

U -235.

2) Need the energy

3) Cut down on chemical and biological pollution.

Against: 1) Breeder reactors much more complex than non-breeders.

2) Transporting dangerous plutonium and other radioactive materials.

3) More processing of dangerous radioactive material;s.

4) More reliance upon nuclear power which is a "dangerous industry".