Physics 0088 Spring 2023 Homework #5
Hello, dear friend, you can consult us at any time if you have any questions, add WeChat: daixieit
Homework #5
Physics 0088
Spring 2023
Due: Thursday, March 23, at 5pm
All problems are worth 5 points.
1. A kiloWatt-hour (kWh) is a unit of energy. Which is closest to 1kWh in Joules?
A. 3000 J
B. 300 J
C. 3,000,000 J
D. 3 J
E. 30 J
2. What do Newton’s Law of gravitation and Coulomb’s Law of static electrical forces have in common?
A. They are both “inverse square” distance laws.
B. They both describe magnetism.
C. They both have the same proportionality constant.
D. They were both discovered by Einstein.
E. They both describe the forces between moving charges.
3. If I move a large number of negatively charged particles (say, electrons) close to one another, I can store energy in their configuration.
A. True
B. False
C. Only if we ignore the force of gravity.
D. False, the particles must have different charges in order to store energy.
E. Only on Tuesdays.
4. In 1820, Hans Christian Ørsted discovered that __________ would deflect a compass needle.
A. gorillas
B. a nearby bar magnet made of iron and nickel
C. a nearby charged particle
D. a nearby lithium battery
E. a nearby electric current
5. Magnetic forces are caused by …
A. static charged particles.
B. conducting metals, such as copper.
C. moving charged particles, such as the electrical current in a wire.
D. the flu virus
E. the motions of positively charged particles, but not the motions of negatively charge particles.
6. In 1831 Michael Faraday discovered …
A. the law of force between two charged particles.
B. the law of force between two currents.
C. the law of conservation of energy.
D. the law of chemical equilibrium.
E. the law of electromagnetic induction.
7. As we discussed in class, which one of these devices works primarily because a current can be used to generate a magnetic field and thus a magnetic force?
A. A Stirling motor heat engine.
B. A loudspeaker used to play music.
C. An electrical generator.
8. Magnetic fields differ from electric fields in the sense that …
A. electric fields always form closed loops, but magnetic field don’t.
B. magnetic fields always form closed loops, but electric fields don’t.
C. they do not differ from one another, they are exactly the same.
9. Which of the following devices work using the law of magnetic induction?
A. Electric guitar pickups.
B. Electric generators.
C. The “flying ring” (aka “Gauss gun”) experiment from class.
D. All of the above.
10. If I could shoot a beam of electrons across the classroom, this beam would give rise to ____________.
A. a magnetic field.
B. an electric field.
C. both a magnetic and an electric field.
D. a magnetic inductor.
E. potential energy.
11. A varying magnetic field creates an electrical current.
A. True.
B. False.
12. A varying electric field causes a magnetic field.
A. True.
B. False.
13. If I supply an electrical motor with 100 W of power, how high could this motor lift a 10kg weight in 1 second (ignoring any friction in the motor)?
A. 0. 1m
B. 1m.
C. 10m.
D. 100m
E. 1000m
14. Let’s say I supply power through power lines to a power customer and that the voltage on the lines is 104 V. In this situation, let’s say that I lose 104 W of power. Now, suppose that I change
the supply voltage to 105 V. How much power do I lose if I deliver power at this new voltage?
A. 10 W
B. 102 W.
C. 103 W.
D. 104 W.
E. 106 W
15. Power transmission lines are maintained a very high voltage (10,000 V to 350,000 V) because…
A. this is the safest operating voltage.
B. this reduces the amount of power that the customer needs to consume.
C. higher voltages minimized the resistance of the wires.
D. higher voltages minimize the amount of energy wasted in the wires during transmission.
16. At a typical power plant, if I provide 1000 MW of power from the burning of a fuel, such as coal or natural gas, approximately how much energy actually gets transformed into electrical energy?
A. 400 MW
B. 1000 MW
C. 900 MW
D. 600 MW
E. 100 MW
17. If I generate electricity by moving a magnet near a wire, I have to keep doing work on the magnet in order to keep generating electricity because (neglect friction) …
A. An electric field is generated in the wire that always acts to prevent the motion of the magnet.
B. A magnetic field is generated by the current in the wire that always acts to prevent the motion of the magnet.
18. For the situation described in question 17, I must keep working on the magnet. The big picture is that this is just an example of conservation of energy.
A. True
B. False
19. Gravitational potential energy can be converted into electrical energy in the form of the kinetic energy of electrons.
A. True
B. False
20. Heat energy can be converted into gravitational potential energy.
A. True B. False.
2023-03-22