Every problem in the chapter beside the book’s answer, a chapter at a time as you scroll.
Chapter 23: Electromagnetic Induction, AC Circuits, and Electrical Technologies
54 problems · 9 figures23-1 §23.1 source ↗
Answer
23-3 §23.2 source ↗
Answer
(a) CCW
(b) CW
(c) No current induced
23-5 §23.2 source ↗
Answer
(a) 1 CCW, 2 CCW, 3 CW
(b) 1, 2, and 3 no current induced
(c) 1 CW, 2 CW, 3 CCW
23-9 §23.2 source ↗
Answer
(b) As a lower limit on the ring, estimate R = 1.00 mΩ. The heat transferred will be 2.31 mJ. This is not a significant amount of heat.
23-11 §23.2 source ↗
Answer
23-13 §23.2 source ↗
Integrated Concepts
Approximately how does the emf induced in the loop in Figure 23.54(b) depend on the distance of the center of the loop from the wire?
Answer
23-17 §23.3 source ↗
Answer
(a) 0.630 V
(b) No, this is a very small emf.
23-19 §23.3 source ↗
Answer
23-25 §23.3 source ↗
Integrated Concepts
The Tethered Satellite discussed in this module is producing 5.00 kV, and a current of 10.0 A flows. (a) What magnetic drag force does this produce if the system is moving at 7.80 km/s? (b) How much kinetic energy is removed from the system in 1.00 h, neglecting any change in altitude or velocity during that time? (c) What is the change in velocity if the mass of the system is 100,000 kg? (d) Discuss the long term consequences (say, a week-long mission) on the space shuttle’s orbit, noting what effect a decrease in velocity has and assessing the magnitude of the effect.
Answer
(a) 10.0 N
(b)
(c) 0.36 m/s
(d) For a week-long mission (168 hours), the change in velocity will be 60 m/s, or approximately 1%. In general, a decrease in velocity would cause the orbit to start spiraling inward because the velocity would no longer be sufficient to keep the circular orbit. The long-term consequences are that the shuttle would require a little more fuel to maintain the desired speed, otherwise the orbit would spiral slightly inward.
23-28 §23.5 source ↗
Answer
23-30 §23.5 source ↗
Answer
23-32 §23.5 source ↗
Answer
(a) 50
(b) yes
23-34 §23.5 source ↗
Answer
(a) 0.477 T
(b) This field strength is small enough that it can be obtained using either a permanent magnet or an electromagnet.
23-36 §23.5 source ↗
Answer
(a) 5.89 V
(b) At t=0
(c) 0.393 s
(d) 0.785 s
23-38 §23.5 source ↗
Unreasonable Results
A 500-turn coil with a area is spun in the Earth’s field, producing a 12.0 kV maximum emf. (a) At what angular velocity must the coil be spun? (b) What is unreasonable about this result? (c) Which assumption or premise is responsible?
Answer
(a)
(b) This angular velocity is unreasonably high, higher than can be obtained for any mechanical system.
(c) The assumption that a voltage as great as 12.0 kV could be obtained is unreasonable.
23-39 §23.6 source ↗
Answer
(a)
(b) 1.67 A
23-41 §23.6 source ↗
Answer
23-43 §23.6 source ↗
Integrated Concepts
The motor in a toy car is powered by four batteries in series, which produce a total emf of 6.00 V. The motor draws 3.00 A and develops a 4.50 V back emf at normal speed. Each battery has a internal resistance. What is the resistance of the motor?
Answer
23-44 §23.7 source ↗
Answer
(a) 30.0
(b)
23-46 §23.7 source ↗
Answer
(a) 20.0 mA
(b) 2.40 W
(c) Yes, this amount of power is quite reasonable for a small appliance.
23-48 §23.7 source ↗
Answer
(a) 0.063 A
(b) Greater input current needed.
23-50 §23.7 source ↗
Answer
(a) 2.2
(b) 0.45
(c) 0.20, or 20.0%
23-52 §23.7 source ↗
Unreasonable Results
The 335 kV AC electricity from a power transmission line is fed into the primary coil of a transformer. The ratio of the number of turns in the secondary to the number in the primary is . (a) What voltage is induced in the secondary? (b) What is unreasonable about this result? (c) Which assumption or premise is responsible?
Answer
(a) 335 MV
(b) way too high, well beyond the breakdown voltage of air over reasonable distances
(c) input voltage is too high
23-54 §23.8 source ↗
Integrated Concepts
A short circuit to the grounded metal case of an appliance occurs as shown in Figure 23.57. The person touching the case is wet and only has a resistance to earth/ground. (a) What is the voltage on the case if 5.00 mA flows through the person? (b) What is the current in the short circuit if the resistance of the earth/ground wire is ? (c) Will this trigger the 20.0 A circuit breaker supplying the appliance?
Answer
(a) 15.0 V
(b) 75.0 A
(c) yes
23-55 §23.9 source ↗
Answer
23-57 §23.9 source ↗
Answer
23-61 §23.9 source ↗
Answer
(a) 31.3 kV
(b) 125 kJ
(c) 1.56 MW
(d) No, it is not surprising since this power is very high.
23-63 §23.9 source ↗
Answer
(a) 1.39 mH
(b) 3.33 V
(c) Zero
23-65 §23.9 source ↗
Answer
23-67 §23.9 source ↗
Integrated Concepts
A very large, superconducting solenoid such as one used in MRI scans, stores 1.00 MJ of energy in its magnetic field when 100 A flows. (a) Find its self-inductance. (b) If the coils “go normal,” they gain resistance and start to dissipate thermal energy. What temperature increase is produced if all the stored energy goes into heating the 1000 kg magnet, given its average specific heat is ?
Answer
(a) 200 H
(b)
23-69 §23.10 source ↗
Answer
23-71 §23.10 source ↗
Answer
23-73 §23.10 source ↗
Answer
23-75 §23.10 source ↗
Answer
23-77 §23.10 source ↗
Answer
(a) 24.6 ms
(b) 26.7 ms
(c) 9% difference, which is greater than the inherent uncertainty in the given parameters.
23-79 §23.11 source ↗
Answer
23-81 §23.11 source ↗
Answer
23-83 §23.11 source ↗
Answer
(a) 2.55 A
(b) 1.53 mA
23-85 §23.11 source ↗
Answer
23-87 §23.11 source ↗
Answer
(a) 21.2 mH
(b)
23-89 §23.11 source ↗
Answer
(a) 3.18 mF
(b)
23-92 §23.12 source ↗
Answer
(a) at 60.0 Hz, at 10.0 kHz
(b) At 60 Hz, with a capacitor, , over 13 times as high as without the capacitor. The capacitor makes a large difference at low frequencies. At 10 kHz, with a capacitor , about the same as without the capacitor. The capacitor has a smaller effect at high frequencies.
23-94 §23.12 source ↗
Answer
(a) at 60.0 Hz, at 10.0 kHz
(b) These values are close to those obtained in Example 23.12 because at low frequency the capacitor dominates and at high frequency the inductor dominates. So in both cases the resistor makes little contribution to the total impedance.
23-96 §23.12 source ↗
Answer
23-98 §23.12 source ↗
Answer
23-100 §23.12 source ↗
Answer
(a)
(b) 1.66 pF
23-102 §23.12 source ↗
Answer
(a)
(b)
(c) 31.9 mA at 500 Hz, 312 mA at 7.50 kHz
(d) 82.2 kHz
(e) 0.408 A
23-104 §23.12 source ↗
Answer
(a) 0.159
(b)
(c) 26.4 W
(d) 166 W
23-106 §23.12 source ↗
Answer
23-107 §23.12 source ↗
Answer
(a)
(b)
(c) The average emf is 0 since the loops are made by a wire that crosses, so the voltage from each loop cancels the emf from the other.
(d) No.
AP Test Prep 23.1 §23.1 source ↗
To produce current with a coil and bar magnet you can:
(a) move the coil but not the magnet.
(b) move the magnet but not the coil.
(c) move either the coil or the magnet.
(d) It is not possible to produce current.
Answer
(c)
AP Test Prep 23.3 §23.5 source ↗
- a.the magnetic flux is at a maximum.
- b.the magnetic flux is at a minimum.
- c.the change in magnetic flux is at a maximum.
- d.the change in magnetic flux is at a minimum.
Answer
AP Test Prep 23.5 §23.7 source ↗
- a.Primary voltage is higher than secondary voltage.
- b.Primary voltage is lower than secondary voltage.
- c.Primary current is higher than secondary current.
- d.Primary current is lower than secondary current.
Answer
AP Test Prep 23.7 §23.8 source ↗
- a.It has more primary turns than secondary turns.
- b.It has fewer primary turns than secondary turns.
- c.It has an equal number of primary and secondary turns.
- d.It can have more, fewer, or an equal number of primary and secondary turns.
Answer
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Problems and answers are adapted from College Physics for AP® Courses 2e by Gregg Wolfe, Erika Gasper, John Stoke, Julie Kretchman, David Anderson and others, OpenStax, and are used under the CC BY-NC-SA 4.0 licence. Access for free at https://openstax.org/books/college-physics-ap-courses-2e/pages/1-connection-for-ap-r-courses. Illustrations: Copyright Rice University, OpenStax, under CC BY-NC-SA 4.0 license. This adaptation is released under the same licence, is non-commercial, and is neither affiliated with nor endorsed by OpenStax or Rice University.