Download Student Text, pp. 504-505

Review
Chapter 13
Understanding Concepts
1. Copy Figure 1 into your notebook and finish drawing the
rest of the field lines. Indicate the polarities of the magnets.
5. The circles in Figure 4 represent a conductor in a coil.
Determine which circles should have a dot and which
an X.
(a)
(b)
N
N
S
S
conductor
S
Figure 4
Figure 1
2. A straight east-west conductor is held near a plotting
compass that is facing north. What direction of the
electric current in the conductor allows the compass
needle to remain stationary if the compass is
(a) beneath the conductor?
(b) above the conductor?
3. The diagram in Figure 2 represents two parallel current-carrying conductors. Determine whether the conductors attract or repel each other. Explain your
reasoning.
6. In Figure 5, a current-carrying conductor is in the
magnetic field of a U-shaped magnet. With the aid
of a diagram, determine the direction in which the
conductor is forced.
N
S
Figure 5
7. The diagram in Figure 6 represents a single loop in a
DC electric motor. Determine the direction of the force
on the loop.
Figure 2
4. Each empty circle in Figure 3 represents a plotting compass near a coiled conductor. Copy the diagrams, label
the N- and S-poles of each coil, and indicate the direction of the needle of each compass.
(a)
compass
S
N
Figure 6
8. Two coils have the same length. One coil has 150 turns
and a current of 2.0 A. The other coil has 300 turns and
a current of 5.0 A. How will the strengths of the two
coils compare?
9. Figure 7 shows one design of an electric relay. Describe
the sequence of events that occur when the switch in
the left-hand circuit is closed.
large current
conductor
coil
(b)
motor, lamp, or
other device
spring
soft iron core
Figure 3
small current
Figure 7
504 Chapter 13
iron bar
10. Each of the diagrams in Figure 8 represents a simple
motor. Copy each diagram and indicate the direction of
the electric current throughout the circuit, the polarity of
the armature, and the direction the armature will turn.
(a)
15. (a) Use the domain theory to explain how a metal
paper clip can become a magnet.
(b) How can the paper clip be demagnetized? Use the
domain theory to explain your method.
(c) How can a paper clip be used as a compass? Does it
matter if the paper clip is magnetized?
16. Explain in your own words how a loudspeaker works.
17. Compare a DC motor and a galvanometer with regard
to how they are constructed and how they work.
Applying Inquiry Skills
N
S
(b)
S
N
Figure 8
11. The domains of magnetic substances are composed of
the atoms of those substances. Which particles within
the atoms (electrons or protons) are likely responsible
for the magnetic properties of domains? What experimental evidence supports your answer?
12. Do electromagnets have a maximum magnetic field
strength that cannot be increased by increasing the
number of loops or the current? Explain.
13. (a) Explain in detail how a galvanometer works.
(b) Why must a voltmeter have a high resistance?
(c) Why must an ammeter have a low resistance?
14. The strength of an electromagnet can be increased by
increasing the current in the coil. How is the magnetic
field around a long straight conductor related to the
electric current in the conductor? Draw two diagrams
of the magnetic fields around two different wires, one
with a large electric current and the other with a small
electric current.
18. (a) Sketch the magnetic field of a current-carrying coil,
showing the direction of the field lines in the core
and marking the magnetic polarities at each end of
the coil.
(b) Draw a sketch of an experimental arrangement that
could be used to magnetize a bar made of iron so
that it would have an S-pole at each end and an
N-pole in the middle.
19. Design and carry out an experiment to discover
whether magnetic field lines pass through paper, aluminum, iron, wood, or any other materials you wish to
try. Discuss how you would design magnetic shielding
to protect a sensitive electric instrument.
20. Design a device that would efficiently magnetize wornout magnets.
21. How can you make a compass without using any magnetic substance? (Hint: Is copper magnetic?)
Making Connections
22. Many refrigerator magnets are flexible and appear to be
made of rubber. How is this type of magnet made?
23. When repairing a broken magnetic tape for a tape
recorder, it is better to use plastic scissors than steel
scissors. Explain.
Exploring
24. Research other devices that use electromagnets using
the Web or any other source. Discuss uses for the
device and how electromagnets are involved. Some
possibilities are telephone earpieces, electromagnet
relays, fusion reactors (torsional), maglev trains, and
particle accelerators. Follow the links for Nelson
Physics 11, Chapter 13 Review.
GO TO
www.science.nelson.com
Electromagnetism 505