Review Questions: Magnetism
Answers
1. The source of all magnetism is
A. tiny pieces of iron.
B. tiny domains of aligned atoms.
C. ferromagnetic materials.
D. moving electric charge.
E. none of these.
2. Magnetic compasses apparently were first used by
A. Columbus.
B. Greeks.
C. Australian aborigines.
D. Vikings.
E. pigeons, then Chinese.
3. Moving electric charges will interact with
A. an electric field.
B. a magnetic field.
C. both of these.
D. none of these.
Reasoning: Moving electric charges will be acted upon by a force due to both electric and magnetic fields.
4. If a steady magnetic field exerts a force on a moving charge, that force is directed
A. opposite the motion.
B. in the direction of the motion.
C. at right angles to the direction of the motion.
5.A transformer can be used to increase the
A. voltage of AC electricity
B. power of AC electricity
C. voltage of DC electricity
D. power of DC electricity
Reasoning: Transformers cannot change the voltage of a DC (like a battery) source. They cannot change the power either.
6. An iron rod becomes magnetic when
A. positive ions accumulate at one end and negative ions at the other end.
B. its atoms are aligned having plus charges on one side and negative charges on the other.
C. the magneic dipoles are in the same direction.
D. its electrons stop moving and point in the same direction.
E. none of these.
Reasoning: See page 464 of your text.
7. Like kinds of magnetic poles repel while unlike kinds of magnetic poles
A. attract.
B. repel also.
C. may attract or repel.
8. Several paper clips dangle from the north pole of a magnet. The induced pole in the bottom of the lowermost paper clip is a
A. north pole.
B. south pole.
C. north or south pole - no difference really.
9. An iron nail is more strongly attracted to the
A. north pole of a magnet.
B. south pole of a magnet.
C. north or south pole - no difference really.
10. Surrounding every moving electron is
A. a magnetic field.
B. an electric field.
C. both of these.
D. none of these.
11. Magnetism is due to the motion of electrons as they
A. move around the nucleus.
B. spin on their axes.
C. both of these.
D. none of these.
12. Magnetic domains normally occur in
A. iron.
B. copper.
C. silver.
D. all of these.
E. none of these.
Reasoning: Copper and silver are NOT magnetic.
13. Magnetic field lines about a current-carrying wire
A. extend radially from the wire.
B. circle the wire in closed loops.
C. both of these.
D. neither of these.
Reasoning: See page 465, figure 24.9.
14. The force on an electron moving in a magnetic field will be the largest when its direction is
A. the same as the magnetic field direction.
B. exactly opposite to the magnetic field direction.
C. perpendicular to the magnetic field direction.
D. at an angle other than 90 degrees to the magnetic field direction.
E. none of these.
15. The intensity of cosmic rays bombarding the Earth's surface is largest at the
A. poles.
B. mid-latitudes.
C. equator.
Reasoning: More particles are enetering the atmosphere near the poles.
16. If we think of the Earth as a magnet, its north (-seeking) pole is nearest
A. the Hudson Bay region of Canada.
B. Australia.
C. both of these.
17. Which pole of a compass needle points to a south pole of a magnet?
A. north pole
B. south pole
C. both of these
18. Neon signs require about 12,000 volts to operate. If the circuit uses a 120-volt power source, the ratio of primary to secondary turns on the transformer should be
A. 1:100.
B. 100:1.
C. neither of these.
19. Magnet A has twice the magnetic field strength of Magnet B and at a certain distance pulls on magnet B with a force of 100 N. The amount of force that magnet A exerts on magnet B is
A. at or about 50 N.
B. exactly 100 N.
C. more information is needed.
Reasoning: Based on the Newton's 3rd law, they apply equal and opposite forces.
20. The primary of a transformer is the coil connected to
A. the load.
B. the Internet.
C. the power line.
D. none of these.
21. Transformers use ac so there will be the required
A. transfer of energy from coil to coil.
B. voltage for transformation.
C. change in magnetic field for operation.
D. change in input current.
E. magnetic field intensities.
22. When a bar magnet is broken in two, each piece is
A. as magnetic as the original magnet.
B. actually stronger than the original magnet.
C. at most half as strong as the original magnet.
D. no longer magnetic.
23. The metal detectors that people walk through at airports operate via
A. Ohm's law.
B. Faraday's law.
C. Coulomb's law.
D. Newton's laws.
E. civil laws.
Reasoning: See chapter 25.
24. A possible cause for the existence of the Earth's magnetic field is
A. moving charges in the liquid part of the Earth's core.
B. great numbers of very slow moving charges in the Earth.
C. convection currents in the liquid part of the Earth's core.
D. all of these.
E. none of these.
25. A device that transforms electrical energy to mechanical energy is a
A. generator.
B. motor.
C. transformer.
D. magnet.
E. none of these.