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Chapter 20 Electromagnetic Induction
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1. A metal rod of length (L) moves with velocity (v), perpendicular to its length, in a magnetic field B, which is
perpendicular to both the rod and its velocity. If the length of the rod is doubled, what happens to the electric
field in the rod?
A. It stays the same.
B. It doubles.
C. It quadruples.
D. It halves.
E. It quarters.
3. A metal rod of length 2.0 m is moved at 6.0 m/s in a direction perpendicular to its length. A 5.0 mT magnetic
field is perpendicular to both the rod and its velocity. What is the potential difference between the ends of the
rod?
A. 12 mV
B. 60 mV
C. 30 mV
D. 15 mV
E. 0
5. A metal rod of length 2.0 m is moved at 6.0 m/s in a direction perpendicular to its length. A 5.0 mT magnetic
field is perpendicular to both the rod and its velocity. If the resistance of the rod is 15 mΩ, what is the current in
the rod?
A. 0.0 A
B. 1.0 A
C. 2.0 A
D. 4.0 A
E. 8.0 A
6. A conducting rod is sliding on metal rails with velocity (v). A magnetic field B is into the paper, the
separation of the rails is L, and the resistance of the circuit is R. In what direction in the diagram is the current
flowing in the resistor?
A. up
B. down
C. up then down
D. down then up
E. insufficient information given
7. A conducting rod slides at 3.0 m/s on metal rails separated by 2.0 m. The 0.66 mT magnetic field is into the
paper. If the resistance is 220 mΩ, what is the current in the circuit?
A. 18 mA
B. 9.0 mA
C. 87 μA
D. 3.0 μA
E. 4.5 mA
17. A 20 turn coil of area 10 cm2 is placed in a magnetic field so that the normal to its area is in the direction of
the field. If the field originally has a value of 0.25 T that increases to 0.35 T in 2.0 s, what is the average emf
induced in the coil?
A. 7.0 mV
B. 2.0 mV
C. 1.0 mV
D. 3.5 mV
E. 4.0 mV
18. The north end of a bar magnet is pushed downward toward a wire loop in the plane of the paper. In which
direction is the induced current, and which way is the induced magnetic field?
A. Clockwise, into the paper
B. Clockwise, out of the paper
C. Counter-clockwise, into the paper
D. Counter-clockwise, out of the paper
E. There is no induced current.
23. A transformer has 200 turns on its primary and 12 turns on its secondary. If the input voltage is 2000 V,
what is the output voltage?
A. 3.3 × 104 V
B. 240 V
C. 170 V
D. 120 V
E. 100 V
25. An ideal transformer has an input voltage of 20,000 V and an output voltage of 260 V. If the input current is
26.0 A, what is the output current?
A. 1.70 A
B. 10.0 A
C. 100 A
D. 200 A
E. 2000 A
28. Eddy current in conductors:
A. step up voltages.
B. dissipate energy.
C. increase currents in circuits.
D. decrease net charges.
E. increase net charges.
31. A solenoid of length 4.00 cm and cross-sectional area 2.00 cm2 has 80 turns. What is its self-inductance?
A. 160 μH
B. 120 μH
C. 80.0 μH
D. 40.0 μH
E. 0.500 μH
33. What is the inductance of a coil that has an emf of 0.82 V induced in it while the current through it is
changing at 2.0 A/s?
A. 3.3 H
B. 33 mH
C. 1.6 H
D. 41 mH
E. 0.41 H
35. If the magnetic energy stored by a 0.50 H inductor is 3.6 J, what is the current through it?
A. 0.13 A
B. 0.90 A
C. 1.8 A
D. 3.8 A
E. 5.4 A
38. The current in a 0.40 H inductor increases form 2.0 A to 3.0 A in 1.5 s. The energy stored by the inductor
during this process increases by:
A. 3.6 J
B. 1.8 J
C. 1.2 J
D. 1.0 J
E. 0.6 J
39. A series LR circuit consists of a battery, resistor, inductor and a switch. When the switch is closed the
circuit has a time constant of 8.0 s. If the resistance and inductance of the circuit are both doubled, what is the
resulting time constant?
A. 8.0 s
B. 16 s
C. 32 s
D. 4.0 s
E. 2.0 s
43. A series LR circuit includes a 9.0 V battery, a resistance of 0.50 Ω, and an inductance of 0.80 H. What is the
current 2.0 s after the switch is closed?
A. 18 A
B. 13 A
C. 6.4 A
D. 5.2 A
E. 4.3 A
48. What is the magnetic energy density in a volume where the magnetic field is 4.0 mT?
A. 3.2 × 10-3 J/m3
B. 3.2 J/m3
C. 6.4 J/m3
D. 13 J/m3
E. 13 × 10-3 J/m3