Magnets Version D
Choose the best answer to each question.
1. Surrounding every moving electron is __________.
A. a magnetic field. B. an electric field. C. both A and B D. none of these
2. A magnet is moved in and out of a coil of wire connected to a high-resistance voltmeter. If the number of coils doubles, the induced
voltage __________.
A. quadruples. B. doubles. C. is the same. D. halves. E. none of these
3. A certain transformer doubles input voltage. If the primary coil has 10 A of current, then the current in the secondary coil is _____.
A. 2 A. B. 5 A. C. 10 A. D. 20 A. E. none of these
4. The force on an electron moving in a magnetic field will be the largest when its direction __________.
A. is the same as the magnetic field direction.
B. is exactly opposite to the magnetic field direction.
C. is perpendicular to the magnetic field direction.
D. is at an angle other than 90 degrees to the magnetic field direction.
E. none of these
5. The earth's magnetic field is most likely due to __________.
A. millions of small magnets buried in the earth.
B. convection currents in the molten part of the earth's interior.
C. the rotation of the earth acting on all of the earth's electrons.
D. a magnetized solid inner core of the earth.
E. none of these
6. Magnetism is due to the motion of electrons as they __________.
A. move around the nucleus. B. spin on their axes. C. both A and B D. none of these
7. Four amps of current exist in the primary coil of a transformer. The voltage across the primary coil is 110 V. What is the approximate
power output of the secondary coil?
A. 27.5 W B. 110 W C. 440 W D. 880 W E. Not enough information to say
8. The earth's magnetic field reverses its polarity about once every __________.
A. million years. B. 100,000 years. C. 100 years. D. The earth's magnetic field never reverses its polarity.
9. If the primary coil of a transformer were connected to a DC power source, the transformer would operate __________.
A. at very low efficiency.
B. the same as always.
C. only if the output is also DC voltage.
D. only while being connected or disconnected.
E. none of these
10. A wire carrying a current is bent into a loop. The magnetic field is strongest __________.
A. at the edges of the loop. B. where the loop is located. C. at the center of the loop.
11. A step-up transformer __________.
A. decreases voltage. B. increases voltage. C. doesn't change the voltage at all.
12. A generator is used to light a bulb. Energy for lighting the bulb actually comes from a __________.
A. coil of wire.
B. mechanical input to the generator.
C. magnet in the generator.
D. plug where the generator is connected to the wall.
E. none of these
13. The principal advantage of AC power over DC power is that __________.
A. less energy is dissipated during transmission.
B. AC voltage oscillates whereas DC voltage does not.
C. AC voltage can be transformed more easily.
D. AC circuits multiply power more easily.
E. AC circuits are safer.
14. In order to make an electromagnet, you need a __________.
A. battery, some wire, and a nail.
B. battery, a nail, and a magnet.
C. magnet, a nail, and some wires.
D. loop of wire, contacts, and a battery.
E. none of these
15. Changing the magnetic field intensity in a closed loop of wires induces __________.
A. current. B. voltage. C. both. D. neither.
16. Magnetic field strength is __________.
A. strongest close to a magnet. B. strongest far from a magnet. C. constant everywhere around a magnet.
17. A transformer works because __________.
A. electricity is induced in a rotating coil.
B. a changing magnetic field is transferred to a coil via an iron core.
C. electricity flows from a primary coil to a secondary coil.
D. electricity is transferred to a coil via an iron core.
18. The voltage across a transformer primary coil that has 100 turns is 10 V. What is the voltage across the secondary coil, which has 20
turns?
A. 100 V B. 50 V C. 10 V D. 5 V E. 2 V
19. The reason a magnet can attract an unmagnetized nail is that __________.
A. nails become permanently magnetized in a magnetic field.
B. nails become temporarily magnetized in a magnetic field.
C. nails really are magnetized.
D. a magnet can't attract anything that isn't also magnetized.
20. A device consisting of a coil that is mechanically rotated in a stationary magnetic field is called __________.
A. a transformer. B. a motor. C. a generator. D. a dipole. E. a magnetic pole.
21. The voltage across the input terminals of a transformer is 110 V. The primary has 50 loops and the secondary has 25 loops. The voltage
the transformer puts out is __________.
A. 25 V. B. 55 V. C. 110 V. D. 220 V. E. none of these
22. The magnetic field strength inside a current-carrying coil will be greater if the coil encloses a __________.
A. vacuum. B. wooden rod. C. glass rod. D. iron rod.
23. Moving electric charges will interact with __________.
A. an electric field. B. a magnetic field. C. both A and B D. none of these
24. An electric motor and an electric generator are __________.
A. very similar devices. B. entirely different devices.
25. Magnetic domains are __________.
A. clusters of atoms randomly aligned. C. regions that may or may not be magnetized.
B. blocks of material. D. regions of atoms magnetically aligned.
26. Which geographic pole of the earth is nearest the magnetic north pole of the earth?
A. North pole B. South pole C. both A and B
27. Magnetic fields are produced by __________.
A. charges at rest. B. moving particles. C. moving particles of earth. D. moving charged particles. E. none of these
28. A magnet is moved in and out of a coil of wire connected to several lamps. If the number of coils is doubled __________.
A. it is easier to move the magnet.
B. it is harder to move the magnet.
C. there is no difference in moving the magnet.
29. The principal reason voltage is induced in the loops of a generator coil is that the __________.
A. loops are rotating, changing the amount of magnetic field within the loops.
B. magnet is rotating.
C. magnet's strength is changing.
D. size of the loops are changing.
E. all of these
30. Most commercial generators are driven by __________.
A. wind. B. rain. C. falling water. D. steam.
31. Which force field can increase a moving electron's speed?
A. Electric field B. Magnetic field C. both A and B D. none of these
32. An electromagnetic wave is composed of __________.
A. vibrating regions of space.
B. regions where charges vibrate a lot.
C. perpendicular electric and magnetic fields vibrating together.
D. transverse vibrations of charges in space.
E. none of these
33. If you put a small compass in a magnetic field, the compass will __________.
A. swing randomly.
B. line up in a direction perpendicular to the magnetic field lines.
C. line up in a direction parallel to the magnetic field lines.
D. seek electrical charge concentrations.
34. When current passes through a wire, a magnetic field is created around the wire only if the __________.
A. current comes from a battery.
B. current makes a complete loop.
C. wire is absolutely straight.
D. wire is curved in a loop.
E. A magnetic field is always created around the wire.
35. The source of all magnetism is __________.
A. tiny pieces of iron.
B. tiny domains of aligned atoms.
C. ferromagnetic materials.
D. moving electric charges.
E. none of these
36. Electromagnetic waves travel at speeds __________.
A. greater than the speed of light. B. equal to the speed of light. C. less than the speed of light.
37. Permanent magnets can be made by __________.
A. stroking material containing iron with a magnet.
B. placing a piece of iron in a strong magnetic field. D. all of these
C. placing a piece of iron near a strong electromagnet. E. none of these
38. A device that uses two coils around an iron core to change the voltage across a circuit is called a __________.
A. voltmeter. B. diode. C. transformer. D. generator. E. motor.
39. A device that transforms electric energy to mechanical energy is a __________.
A. generator. B. motor. C. transformer. D. magnet. E. none of these
40. Magnetic field lines surrounding a magnet are conventionally drawn __________.
A. from north to south. B. from south to north. C. either way.
41. Loops of wire in a motor rotate because a __________.
A. battery effectively pushes a loop around in the field.
B. magnet attracts stationary electrons in the wire. D. current exerts a force on the loop, causing it to rotate.
C. magnetic field exerts forces on moving electrons in the loop. E. none of these
42. The magnetic pole in the Northern Hemisphere is located __________.
A. at the geographic North Pole. B. in Alaska. C. in Canada. D. just north of the United States. E. none of these
43. A transformer transforms __________.
A. magnetic field lines. B. generators into motors. C. non-safe forms of energy into safe forms. D. voltage.
44. If a magnet is pushed into a coil, voltage is induced across the coil. If the same magnet is pushed into a coil with twice the number of
loops __________.
A. one half as much voltage is induced.
B. the same voltage is induced.
C. twice as much voltage is induced.
D. four times as much voltage is induced.
E. none of these
45. If a compass is moved from the Northern Hemisphere to the Southern Hemisphere, its magnetic needle will change direction ___.
A. by 180 degrees. B. by 90 degrees. C. not at all. D. none of these
46. The intensity of cosmic rays bombarding the earth's surface is largest at the __________.
A. poles. B. mid-latitudes. C. equator.
47. If the north pole of one magnet is brought near the south pole of another magnet, the poles will __________.
A. attract each other.
B. repel each other.
C. not interact with each other at all.
48. If you break a bar magnet in half, each half __________.
A. contains one magnetic pole.
B. becomes a bar magnet with two poles.
C. becomes unmagnetized.
49. Cross-country power lines carry voltages of about __________.
A. 120 000 V. B. 2200 V. C. 120 V. D. 60 V.
50. The phenomenon of inducing voltage by changing the magnetic field around a conductor is called __________.
A. generated voltage.
B. Faraday's induction. D. transformer induction.
C. electromagnetic radiation. E. electromagnetic induction.