Chapter
21 Sample Multiple Choice Problems
1. A circular loop of radius 0.10 m is rotating in a uniform
magnetic field of 0.20 T. Find the
magnetic flux through the loop when the plane of the loop and the magnetic
field vector are parallel.
a. zero
b. 3.1X10-3
Tm2
c. 5.5X10-3
Tm2
d. 6.3X10-3
Tm2
2. A circular loop of radius 0.10 m is rotating in a uniform
magnetic field of 0.20 T. Find the magnetic
flux through the loop when the plane of the loop and the magnetic field vector
are perpendicular.
a. zero
b. 3.1X10-3
Tm2
c. 5.5X10-3
Tm2
d. 6.3X10-3
Tm2
3. A coil is wrapped with 200 turns of wire on a square frame
with sides 18 cm. A uniform magnetic
field is applied perpendicular to the plane of the coil. If the field changes uniformly from 0.50 T to
0 in 8.0 s, find the average value of the induced emf.
a. 2.1 mV
b. 4.1 mV
c. 0.21 V
d. 0.41 V
4. A square coil of wire with 15 turns and an area of 0.40 m2
is placed parallel to a magnetic field of 0.75 T. The coil is flipped so its plane is
perpendicular to the magnetic field in 0.050 s.
What is the magnitude of the average induced emf?
a. 6.0 V
b. 36 V
c. 45 V
d. 90 V
5. The cross-sectional area of an adjustable single loop is
reduced from 1.0 m2 to 0.25 m2 in 0.10 s. What is the average emf
that is induced in this coil if it is in a region where B = 2.0 T upward, and
the coil's plane is perpendicular to B?
a. 12 V
b. 15 V
c. 18 V
d. 21 V
6. Doubling the number of loops of wire in a coil produces what
kind of change on the induced emf, assuming all other
factors remain constant?
a. The induced emf is
4 times as much.
b. The induced emf is
3 times as much.
c. The induced emf is
twice as much.
d. There is no change in the induced emf.
7. A circular loop of wire is rotated at constant angular speed
about an axis whose direction can be varied.
In a region where a uniform magnetic field points straight down, what
must be the orientation of the loop's axis of rotation if the induced emf is to be zero?
a. Any horizontal orientation will do.
b. It must make an angle of 45ø to the vertical.
c. It must be vertical.
d. None of the above.
8. According to Lenz's law, the direction of an induced current
in a conductor will be that which tends to produce which of the following
effects?
a. enhance the effect
which produces it.
b. produce a greater
heating effect.
c. produce the
greatest voltage.
d. oppose the effect
which produces it.
9. An transformer consists of a
500-turn primary coil and a 2000-turn secondary coil. If the current in the secondary is 3.0 A,
what is the current in the primary?
a. 0.75 A
b. 1.3 A
c. 12 A
d. 48 A
10. The potential across an ideal inductor is proportional to
a. the current
flowing through it.
b. the resistance of
the circuit.
c. the rate of change
of current in the coil.
d. None of the above.
11. A transformer is a device that
a. operates on either
DC or AC.
b. operates only on
AC.
c. operates only on
DC.
d. increases the
power level of a circuit.
12. A generator produces 60 A of current at 120 V. The voltage is usualy
stepped up to 4500 V by a transformer and transmitted through a power line of
total resistance 1.0 Ω. Find the
number of turns in the secondary if the primary has 200 turns.
a. 5
b. 200
c. 4500
d. 7500
13. What current flows in a 60-mH inductor when 120 V AC at a frequency
of 20 kHz is applied to it?
a. 8.0 mA
b. 16 mA
c. 24 mA
d. 32 mA
14. Consider an RLC circuit that is driven by an AC applied
voltage. At resonance,
a. the peak voltage
across the capacitor is greater than the peak voltage across the inductor.
b. the peak voltage
across the inductor is greater than the peak voltage across the capacitor.
c. the current is in
phase with the driving voltage.
d. the peak voltage
across the resistor is equal to the peak voltage across the inductor.
15. What is the current through a 0.0010-æF capacitor at 1000 Hz and
5.0 V?
a. 5.4 æA
b. 31 æA
c. 3.1 mA
d. 10 mA
Answers:
1. a
2. d
3. d
4. d
5. b
6. c
7. c
8. d
9. c
10. c
11. b
12. d
13. b
14. c
15. b