Fig. 20-3, p.662
FIGURE 20.3 An edge view of a loop in a uniform magnetic field. (a) When
the field lines are perpendicular to the plane of the loop, the magnetic flux
through the loop is a maximum and equal to ΦB = BA. (b) When the field
lines are parallel to the plane of the loop, the magnetic flux through the loop
is zero.
1
Fig. 20-1, p.661
FIGURE 20.1 Faraday’s experiment. When the switch in the primary circuit
at the left is closed, the ammeter in the secondary circuit at the right
measures a momentary current. The emf in the secondary circuit is induced
by the changing magnetic field through the coil in that circuit.
2
Fig. 20-10, p.666
FIGURE 20.10 (a) In an electric guitar, a vibrating string induces a voltage in
the pickup coil. (b) Several pickups allow the vibration to be detected from
different portions of the string.
3
Fig. 20-12, p.667
FIGURE 20.12 A straight conductor of length l moving with velocity v through
a uniform magnetic field B directed perpendicular to v. The vector Fm is the
force due to magnetism applied to an electron in the conductor. An emf of
vlB is induced between the ends of the bar.
4
Fig. 20-14, p.668
FIGURE 20.14 As the bar moves to the right, the area of the loop increases
by the amount l∆x and the magnetic flux through the loop increases by Bl∆x.
5
Fig. 20-16, p.671
FIGURE 20.16 (a) As the conducting bar slides on the two fixed conducting
rails, the magnetic flux through the loop increases with time. By Lenz’s law,
the induced current must be counterclockwise so as to produce a
counteracting flux out of the paper. (b) When the bar moves to the left, the
induced current must be clockwise. Why?
6
Fig. 20-13, p.667
FIGURE 20.13 (a) A conducting bar sliding with velocity v along two
conducting rails under the action of an applied force Fapp. The magnetic
force Fm opposes the motion, and a counterclockwise current is induced in
the loop. (b) The equivalent circuit of that in (a).
7
Fig. 20-17, p.671
FIGURE 20.17 (a) When the magnet is moved toward the stationary
conducting loop, a current is induced in the direction shown. (b) This induced
current produces its own flux to the left to counteract the increasing external
flux to the right. (c) When the magnet is moved away from the stationary
conducting loop, a current is induced in the direction shown. (d) This induced
current produces its own flux to the right to counteract the decreasing
external flux to the right.
8
Fig. 20-18, p.672
FIGURE 20.18 An example of Lenz’s law.
9
Fig. 20-19, p.672
FIGURE 20.19 (a) Major parts of a magnetic tape recorder. If a new
recording is to be made, the bulk erase head wipes the tape clean of signals
before recording. (b) The fringing magnetic field magnetizes the tape during
recording.
10
Fig. 20-19b, p.672
FIGURE 20.19 (b) The fringing magnetic field magnetizes the tape during
recording.
11
Fig. 20-20, p.673
FIGURE 20.20 (a) A schematic diagram of an AC generator. An emf is
induced in a coil, which rotates by some external means in a magnetic field.
(b) A plot of the alternating emf induced in the loop versus time.
12
Fig. 20-22, p.675
FIGURE 20.22 (a) A schematic diagram of a DC generator. (b) The emf
fluctuates in magnitude, but always has the same polarity.
13
Fig. 20-24, p.677
FIGURE 20.24 After the switch in the circuit is closed, the current produces
its own magnetic flux through the loop. As the current increases towards its
equilibrium value, the flux changes in time and induces an emf in the loop.
The battery drawn with dashed lines is a symbol for the selfinduced emf.
14
Fig. 20-25, p.678
FIGURE 20.25 (a) A current in the coil produces a magnetic field directed to
the left. (b) If the current increases, the coil acts as a source of emf directed
as shown by the dashed battery. (c) The induced emf in the coil changes its
polarity if the current decreases.
15
Fig. 20-27, p.680
FIGURE 20.27 A series RL circuit. As the current increases towards its
maximum value, the inductor produces an emf that opposes the increasing
current.
16
Fig. 20-28, p.681
FIGURE 20.28 A plot of current versus time for the RL circuit shown in figure
20.27. The switch is closed at t = 0, and the current increases towards its
maximum value ε/R. The time constant τ is the time it takes the current to
reach 63.2% of its maximum value.
17
Fig. 20-29, p.681
FIGURE 20.29 (Quick Quiz 20.5)
18
Fig. P20-10, p.684
Fig. P20-18, p.687
Fig. P20-23, p.687
Fig. P20-24, p.687
Fig. P20-25, p.687
Fig. P20-28, p.688
Fig. P20-29, p.688
Fig. P20-51, p.689
Fig. P20-53, p.690
Fig. P20-58, p.690
Fig. P20-60, p.691
Fig. P20-61, p.691
Fig. P20-62, p.691
Fig. P20-63, p.691
Fig. P20-65, p.692