Multiple Choice
Identify the
letter of the choice that best completes the statement or answers the question.
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1.
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A
current can be induced in a closed circuit without the use of a battery or an electrical power supply
by moving the circuit through a a. | high temperature field. | c. | magnetic field. | b. | gravitational
field. | d. | nuclear
field. | | | | |
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2.
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A
loop of wire is held in a vertical position at the equator with the face of the loop facing in the
east-west direction. What change will induce the greatest current in the loop? a. | raising the loop
to a higher elevation | b. | moving the loop north | c. | rotating the
loop so its face is vertical | d. | rotating the loop so its face is
north-south | | |
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3.
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A bar
magnet falls through a loop of wire with constant velocity, and the north pole enters the loop first.
The induced current will be greatest when the magnet is located so that the loop is a. | near either the
north or the south pole. | b. | near the north pole only. | c. | near the middle
of the magnet. | d. | With no acceleration, the induced current is
zero. | | |
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4.
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Electricity may be generated by rotating a loop of wire between the poles of a magnet.
The induced current is greatest when a. | the plane of the loop is parallel to the magnetic
field. | b. | the plane of the loop is perpendicular to the magnetic
field. | c. | the magnetic flux through the loop is a
minimum. | d. | the plane of the loop makes an angle of 45° with the
magnetic field. | | |
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5.
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A
loop of wire is rotated 360° across an external magnetic field. During one period of revolution,
the induced current changes in a. | magnitude only. | c. | both magnitude and direction. | b. | direction
only. | d. | amplitude. | | | | |
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6.
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According to Lenz’s law, the magnetic field of an induced current in a conductor
will a. | enhance the
applied field. | b. | heat the conductor. | c. | increase the
potential difference. | d. | oppose a change in the applied magnetic
field. | | |
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7.
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Which
statement is correct? a. | The magnetic field of an induced current increases the
approaching magnetic field. | b. | According to the principle of energy conservation, an induced
field attempts to keep the total field strength constant. | c. | An induced
electric field opposes an applied magnetic field. | d. | Lenz’s law
is used to find the average induced emf. | | |
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8.
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According to Lenz’s law, if the applied magnetic field changes, a. | the induced
field attempts to keep the total field strength constant. | b. | the induced
field attempts to increase the total field strength. | c. | the induced
field attempts to decrease the total field strength. | d. | the induced
field attempts to oscillate about an equilibrium value. | | |
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9.
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A
coil with 150 turns and a cross-sectional area of  experiences a magnetic field whose
strength increases by +0.65T in 1.80 s. The plane of the coil is perpendicular to the plane of the
applied magnetic field. What is the induced emf in the coil? a. | 54
V | c. |  27
V | b. | 0.36
V | d. |  54
V | | | | |
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10.
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The
operation of an electric motor depends on a. | the Doppler effect. | b. | the
photoelectric effect. | c. | the magnetic force acting on a current-carrying wire in a
magnetic field. | d. | induced commutators from the rotation of a wire in a magnetic
field. | | |
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11.
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How
is a motor’s mechanical energy able to perform mechanical work? a. | Mechanical
energy is converted into electrical energy. | b. | A current is
generated by a rotating loop in a magnetic field. | c. | Electrical
energy is converted into a magnetic force. | d. | A shaft connected to the rotating coil is attached to some
external device. | | |
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12.
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An
electric current that changes directions at regular intervals is called a. | directional
current. | c. | reversible
current. | b. | alternating current. | d. | fluctuating current. | | | | |
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13.
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Which
of the following determines the maximum generated emf in an ac generator? a. | the coil
rotation rate or angular frequency | b. | the magnetic field strength, B | c. | the loop area,
A | d. | all of the above | | |
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Use
the following equations to find maximum emf.
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14.
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A
generator consists of 10.0 turns of wire, and each turn has an area of  . If a maximum emf
of  is induced when the coil rotates with a frequency of 60.0 Hz, what is the strength of the
magnetic field? a. | 0.15
T | c. | 0.85
T | b. | 0.34
T | d. | 1.5
T | | | | |
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15.
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Which
conversion process is the basic function of the electric generator? a. | mechanical
energy to electrical energy | c. | low emf to high
emf, or vice versa | b. | electrical energy to mechanical
energy | d. | alternating
current to direct current | | | | |
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16.
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Two
loops of wire are arranged so that a changing current in the primary will induce a current in the
secondary. The secondary loop has twice as many turns as the primary loop. As long as the current in
the primary is steady at 3.0 A, the current in the secondary will be a. | 6.0
A. | c. | 1.5
A. | b. | 3.0
A. | d. | zero. | | | | |
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17.
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All
of the following statements about ac rms values and maximum values are true except which
one? a. | Rms values may
equal maximum values. | b. | Rms values are always less than maximum
values. | c. | Rms values are approximately 70 percent of the maximum
values. | d. | Rms values are different from maximum values because the
alternating current is at its maximum only for an instant. | | |
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18.
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A
step-down transformer has 2500 turns on its primary and 5.0 ´ 10 turns on its secondary. If
the potential difference across the primary is 4850 V, what is the potential difference across the
secondary? a. | 1.0
V | c. | 110
V | b. | 97
V | d. | 240
V | | | | |
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19.
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How
does an electromagnetic wave propagate itself? a. | A changing magnetic field induces an electric field
perpendicular to the magnetic field. | b. | A changing electric field induces a magnetic field
perpendicular to the electric field. | c. | Changing electric and magnetic fields produce a transverse wave
that is perpendicular to both of the oscillating fields. | d. | all of the
above | | |
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20.
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All
of the following statements about the electromagnetic force are true except which
one? a. | It is one of the
four fundamental forces in the universe. | b. | It exerts a force on either charged or uncharged
particles. | c. | It obeys the inverse-square law. | d. | It is produced
by—and produces—electric and magnetic fields. | | |
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