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36. A current-carrying wire has a magnetic field around 44. The speaker in a stereo system works by the action of
it because a. a permanent magnet creating an electric current.
a. a moving charge produces a magnetic field of its own. b. an electromagnet pushing and pulling on a permanent
b. the current aligns the magnetic domains in the metal of magnet.
the wire. c. sound waves pushing and pulling on an electromagnet.
c. the metal was magnetic before the current was established, d. electrons creating sound waves.
and the current enhanced the magnetic effect. 45. Electromagnetic induction takes place because
d. None of the above is correct. a. an electric current is measured by the rate of movement
37. When an object acquires a negative charge, it actually of charges.
a. gains mass. b. the potential is determined by how much work is done.
b. loses mass. c. electrons have their own magnetic field, which interacts with
c. has a constant mass. an externally applied magnetic field.
d. The answer is unknown. d. copper wire is magnetic, which induces magnetism.
38. A positive and a negative charge are initially 2 cm apart. What 46. The current in the secondary coil of a transformer is
happens to the force on each as they are moved closer and closer produced by a
together? The force a. varying magnetic field.
a. increases while moving. b. varying electric field.
b. decreases while moving. c. constant magnetic field.
c. remains constant. d. constant electric field.
d. The answer is unknown. 47. An electromagnet uses
39. To be operational, a complete electric circuit must contain a a. a magnetic field to produce an electric current.
source of energy, a device that does work, and b. an electric current to produce a magnetic field.
a. a magnetic field. c. a magnetic current to produce an electric field.
b. a conductor from the source to the working device and d. an electric field to produce a magnetic current.
another conductor back to the source. 48. A transformer
c. connecting wires from the source to the working device. a. changes the voltage of a direct current.
d. a magnetic field and a switch. b. changes the power of a direct current.
40. Which variable is inversely proportional to the resistance? c. changes the voltage of an alternating current.
a. Length of conductor d. changes the amperage of an alternating current.
b. Cross-sectional area of conductor 49. A parallel circuit has
c. Temperature of conductor a. wires that are lined up side by side.
d. Conductor material b. the same current flowing through one resistance
41. Which of the following is not considered to have strong magnetic after another.
properties? c. separate pathways for the current to flow through.
a. Iron d. none of the above.
b. Nickel 50. In which type of circuit would you expect a reduction of the
c. Silver available voltage as more and more resistances are added to the
d. Cobalt circuit?
42. A piece of iron can be magnetized or unmagnetized. This is a. Series circuit
explained by the idea that b. Parallel circuit
a. electrons in iron atoms are spinning and have magnetic fields c. Open circuit
around them. d. None of the above
b. atoms of iron are grouped into tiny magnetic domains that 51. In which type of circuit would you expect the same voltage with
may orient themselves in a particular direction or in a an increased current as more and more resistances are added to
random direction. the circuit?
c. unmagnetized iron atoms can be magnetized by an external a. Series circuit
magnetic field. b. Parallel circuit
d. the north and south poles of iron can be segregated by the c. Open circuit
application of an external magnetic field. d. None of the above
43. Earth’s magnetic field is believed to originate
Answers
a. by a separation of north and south monopoles due to currents
1. a 2. c 3. a 4. a 5. b 6. a 7. b 8. c 9. b 10. c 11. a 12. b 13. a 14. d 15. d
within Earth.
16. a 17. a 18. c 19. a 20. a 21. b 22. d 23. c 24. a 25. a 26. b 27. d
b. with electric currents that are somehow generated in Earth’s
28. a 29. b 30. d 31. b 32. a 33. c 34. d 35. c 36. a 37. a 38. a 39. b
core.
40. b 41. c 42. b 43. b 44. b 45. c 46. a 47. b 48. c 49. c 50. a 51. b
c. from a giant iron and cobalt bar magnet inside Earth.
d. from processes that are not understood.

174 CHAPTER 6 Electricity 6-36