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An RL circuit in which L = 0.4 H and R = 5 W is
connected to a battery with E = 22 V at time t = 0. What
energy is stored in the inductor when the current in the
circuit is 0.5 A?
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500 mJ
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2.0 J
5.0 J
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You can calculate the induced current in a ring by setting the emf
from a changing flux E = -DØ/Dt equal to the voltage change LDI/Dt in an inductor. If the magnetic field through a ring of area 1
cm2 collapses from 0.02 T to zero and the inductance of the ring is
10-7 H, what is the induced current in the ring?
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5A
10 A
15 A
20 A
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Superconductors have been discussed as a means for electrical
energy storage. Because they are resistanceless, a current once
started in a loop would continue without loss. If a current of 104 A
were started in a huge toroidal coil of radius 1 km and inductance
50 H, how much electrical energy (in kW hours) could be stored?
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300 kWH
482 kWH
694 kWH
842 kWH
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A small airplane with a wing span of 12 m flies horizontally and due
north at a speed of 60 m/s in a region where the magnetic field of
the earth is 60 µT directed 60° below the horizontal. What is the
magnitude of the induced emf between the ends of the wing?
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50 mV
31 mV
37 mV
44 mV
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What is the minimum frequency with which a 200-turn,
flat coil of cross-sectional area of 300 cm2 can be
rotated in a uniform 30-mT magnetic field if the
maximum value of the induced emf is to equal 8.0 V?
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7.5 Hz
7.1 Hz
8.0 Hz
8.4 Hz
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A series circuit contains a 12-V battery, a 2000 W
resistor, and a 3 mH inductor. If the switch to the battery
is closed at t = 0, find the time required for the current in
the circuit to reach 63% of its final value.
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1.5 ms
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5.0 ms
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A circular loop (area = 0.20 m2 ) turns in a uniform magnetic field
with B = 0.13 T. At an instant when the angle between the magnetic
field and the normal to the plane of the loop is π rads and is
decreasing at the rate of 0.50 rad/s, what is the magnitude of the
emf induced in the loop?
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zero
13 mV
26 mV
20 mV
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A flat coil of wire consisting of 20 turns, each with an area of 50
cm2, is positioned perpendicularly to a uniform magnetic field that
increases its magnitude at a constant rate from 2.0 T to 6.0 T in 2.0
s. If the coil has a total resistance of 0.40 W, what is the magnitude
of the induced current?
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70 mA
140 mA
500 mA
800 mA
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A planar loop consisting of four turns of wire, each of which
encloses 200 cm2, is oriented perpendicularly to a magnetic field
that increases uniformly in magnitude from 10 mT to 25 mT in a
time of 5.0 ms. What is the resulting induced current in the coil if
the resistance of the coil is 5.0 W?
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60 mA
12 mA
0.24 mA
48 mA
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A rectangular loop (area = 0.15 m2 ) turns in a uniform magnetic
field with B = 0.20 T. At an instant when the angle between the
magnetic field and the normal to the plane of the loop is π/2 rads
and increasing at the rate of 0.60 rad/s, what is the magnitude of
the emf induced in the loop?
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24 mV
zero
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30 mV
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The magnet moving past an object will
produce eddy currents in the object if the
object is?
1. magnetic material
only
2. a conductor
3. an insulator
4. a liquid
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If a bar magnet is falling through a loop of wire, the
induced current in the loop of wire sets up a field which
exerts a force on the magnet. This force between the
magnet and the loop will be attractive when?
1. the magnet enters
the loop
2. the magnet is half
way through
3. the magnet is
leaving the loop
4. never
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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?
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the plane of the loop is parallel to
the magnetic field
the plane of the loop is
perpendicular to the magnetic field
the magnetic flux through the loop
is a maximum
the plane of the loop makes an
angle of 45° with the magnetic field
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The "back emf" of a motor refers
to a source of voltage that?
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occurs when the motor
runs backwards
occurs when the motor is
used as a generator
is biggest when the
current through the motor
is biggest
is biggest when the motor
turns fastest
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The magnetic field going through a stationary circular loop
increases from zero to 5 T in a certain time t. The induced current
in the loop will depend on the radius of the loop, r, the resistance of
the loop, R, and the time, t. If two of these stay constant, the
induced current will be directly proportional to?
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t
r
R
none of these
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Two loops of wire are arranged so that a changing current in one,
the primary, will induce a current in the other, the secondary. The
secondary loop has twice as many turns as the primary loop. The
current in the primary at this moment is 3 A and increasing. The
current in the secondary must be?
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3A
6A
zero
there is insufficient
information to work
this problem.
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A metal rod is falling toward the surface of the earth near the
equator. As it falls, one end of the rod becomes positively charged
due to the motional emf of the rod through the earth's magnetic
field. The rod is oriented so that?
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the rod is vertical with the
positive end higher.
the rod is horizontal with the
positive end toward the north.
the rod is horizontal with the
positive end toward the east.
the rod is horizontal with the
positive end toward the west.
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Two loops of wire are arranged so that a changing current in one,
the primary, will induce a current in the other, 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 amps, the current in
the secondary will be?
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3A
6A
1.5 A
zero
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A bar magnet is falling through a loop of wire with
constant velocity with the north pole entering first. The
induced current will be greatest when the magnet is
located so that the loop is?
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near either the north or
the south pole.
near the north pole only
near the middle of the
magnet.
with no acceleration, the
induced current is zero.
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A bar magnet is falling through a loop of wire with
constant velocity with the north pole entering first. As
the south pole leaves the loop of wire the induced
current will be, as viewed from above?
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clockwise
counterclockwise
zero
along the length of
the magnet
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Two loops of wire are arranged so that a changing
current in one will induce a current in the other. If the
current in the first is increasing clockwise by one amp
every second, the current in the second loop will?
1. be increasing
counterclockwise
2. stay constant
3. increase clockwise
also
4. stay zero
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A bar magnet is falling through a loop of wire with
constant velocity with the north pole entering first. As
the north pole enters the wire, the induced current will
be, as viewed from above
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clockwise
counterclockwise
zero
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the magnet
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A 12 V battery is connected in series with a switch, 6 W
resistor and coil. What energy is stored in the coil when
the current is 2.0 A? The time constant is 4 x 10-4 s.
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4.8 x 10-3 J
9.6 x 10-3 J
14.4 x 10-3 J
29 x 10-3 J
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An electric motor draws a current of 2.5 A from a 15 V battery when
it runs at normal speed. If the motor's armature is "jammed" so that
it cannot rotate, the current suddenly rises to 10 A. What is the
back emf of the motor when running at normal speed?
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18.8 V
10.0 V
12.5 V
11.3 V
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A 12 V battery is connected in series with a switch,
resistor and coil. If the circuit's time constant is 4 x 10-4
s and the final steady current after the switch is closed
becomes 2.0 A, what is the value of the inductance?
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1.2 mH
2.4 mH
9.6 mH
48 mH
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A loop of wire is held in a vertical position at the
equator, with the axis of the loop pointing in the eastwest direction. Which change will induce the greatest
current in the loop?
1. raising the loop to a
higher elevation
2. moving the loop north
3. rotating the loop so its
axis is vertical
4. rotating the loop so its
axis is north-south
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By what factor is the self-inductance of an
air solenoid changed if its number of coil
turns, N, is tripled?
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By what factor is the self-inductance of an
air solenoid changed if its cross-sectional
area, A, is tripled?
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What is the self-inductance in a coil which
experiences a 1.5 V induced emf when the
current is changing at a rate of 55 A/s?
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83 mH
45 mH
37 mH
27 mH
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By what factor is the self-inductance of an
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number of coil turns are both tripled?
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An RL series circuit has the following components: 2.5
mH coil, 0.5 ohm resistor, 6.0 V battery, ammeter and
switch. What is the time constant of this circuit?
25% 25% 25% 25%
1.
2.
3.
4.
12.5 x 10-3 s
5 x 10-3 s
2.5 x 10-2 s
200 s
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
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46
47
48
49
50
An RL series circuit has the following components: 2.5
mH coil, 0.5 ohm resistor, 6.0 V battery, ammeter and
switch. After the switch has been closed for a long time,
what is the final value of the current?
25% 25% 25% 25%
1.
2.
3.
4.
2.5 A
12 A
0.015 A
2400 A
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
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41
42
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44
45
46
47
48
49
50
A 0.20 m wire is moved perpendicular to a 0.5
magnetic field at a speed of 1.5 m/s. What emf
is induced across the ends of the wire?
25% 25% 25% 25%
1.
2.
3.
4.
2.25 V
1.0 V
0.60 V
0.15 V
1
2
3
4
1
2
3
4
5
6
7
8
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48
49
50
An airplane with a wingspan of 60 m flies parallel to the earth's
surface at a point where the downward component of the earth's
magnetic field is 0.4 x 10-4 T. If the induced potential between
wingtips is 0.90 V, what is the plane's speed?
25% 25% 25% 25%
1.
2.
3.
4.
250 m/s
338 m/s
375 m/s
417 m/s
1
2
3
4
1
2
3
4
5
6
7
8
9
10
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41
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46
47
48
49
50
A motor with a coil resistance of 10 ohms is supplied by
a voltage of 90 V. What is the current in the motor when
it is running at its maximum speed with a back emf of 60
V?
25% 25% 25% 25%
1.
2.
3.
4.
zero
3.0 A
6.0 A
15.0 A
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
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31
32
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37
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40
41
42
43
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45
46
47
48
49
50
A 500 turn circular coil with an area of 0.05 m2 is mounted on a
rotating frame which turns at a rate of 20 rad/s in the presence of a
0.05 T uniform magnetic field which is perpendicular to the axis of
rotation. What is the instantaneous emf in the coil at the moment
that the normal to its plane is at a 30° angle to the field?
25% 25% 25% 25%
1.
2.
3.
4.
zero
12.5 V
21.6 V
25.0 V
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
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22
23
24
25
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32
33
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35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
A coil with a self-inductance of 0.75 mH experiences a
constant current build up from zero to 5.0 A in 0.125 s.
What is the induced emf during this interval?
25% 25% 25% 25%
1.
2.
3.
4.
0.045 V
0.03 V
0.47 V
0.019 V
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
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19
20
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22
23
24
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28
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32
33
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35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
A 500 turn circular coil with an area of 0.05 m2 is mounted on a
rotating frame which turns at a rate of 20 rad/s in the presence of a
0.05 T uniform magnetic field which is perpendicular to the axis of
rotation. What is the instantaneous emf in the coil at the moment
that the normal to its plane is parallel to the field?
25% 25% 25% 25%
1.
2.
3.
4.
zero
125 V
216 V
250 V
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
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22
23
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25
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32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
A 500 turn circular coil with an area of 0.05 m2 is mounted on a
rotating frame which turns at a rate of 20 rad/s in the presence of a
0.05 T uniform magnetic field which is perpendicular to the axis of
rotation. What is the instantaneous emf in the coil at the moment
that the normal to its plane is at a 90° angle to the field?
25% 25% 25% 25%
1.
2.
3.
4.
zero
12.5 V
21.6 V
25.0 V
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
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23
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31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
A circular coil with an area of 0.05 m2 is wrapped with 500 turns of
wire and is placed in a uniform magnetic field perpendicular to its
plane. If the field changes in value from -0.10 T to +0.15 T in an
interval of 0.5 s, what average voltage is induced in the coil?
25% 25% 25% 25%
1.
2.
3.
4.
12.5 V
125 V
188 V
250 V
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
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23
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31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
How is the energy stored in a current
carrying inductor related to its selfinductance, L?
25% 25% 25% 25%
1.
2.
3.
4.
directly proportional to L2
directly proportional to L1/2
directly proportional to L
inversely proportional to L
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
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32
33
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36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
How is the energy stored in a current
carrying inductor related to the current
value, I?
25% 25% 25% 25%
1.
2.
3.
4.
directly proportional to I2
directly proportional to I1/2
directly proportional to I
inversely proportional to I
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
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41
42
43
44
45
46
47
48
49
50
A uniform 1.5 T magnetic field passes perpendicular
through the plane of a wire loop 0.3 m2 in area. What
flux passes through the loop?
25% 25% 25% 25%
1.
2.
3.
4.
5 Wb
0.45 Wb
0.25 Wb
0.135 Wb
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
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39
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41
42
43
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46
47
48
49
50
A uniform 1.5 T magnetic field passes through the plane
of a wire loop 0.3 m2 in area. What flux passes through
the loop when the direction of the 1.5 T field is at a 30°
angle to the normal of the loop plane?
25% 25% 25% 25%
1.
2.
3.
4.
5 Wb
0.52 Wb
0.39 Wb
0.225 Wb
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
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46
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48
49
50
In a circuit made up of inductor, resistance, ammeter,
battery and switch in series, at which one of the
following time intervals after the switch is closed will the
rate of current increase be greatest?
25% 25% 25% 25%
1. zero
2. one time constant
3. reciprocal of one
time constant
4. ten time constants
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
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31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
The basic function of the electric
generator is which one of the following
conversion processes?
1. mechanical energy to
electrical
2. electrical energy to
mechanical
3. low voltage to high or
vice versa
4. alternating current to
direct
25% 25% 25% 25%
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
The principle or law which says that an induced emf in a
circuit loop produces a current whose magnetic field
opposes further change of magnetic flux, is credited to
which one of the following scientists?
25% 25% 25% 25%
1.
2.
3.
4.
Faraday
Lenz
Ampere
Volta
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
The function of the electric motor is which
one of the following conversion
processes?
1. mechanical energy to
electrical
2. electrical energy to
mechanical
3. low voltage to high or
vice versa
4. alternating current to
direct
25% 25% 25% 25%
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
The back emf in an electric motor is its
maximum value under which of the
following conditions?
25% 25% 25% 25%
1.
2.
3.
4.
motor speed is zero
current is a maximum
voltage is a maximum
motor speed is
maximum
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
In a circuit made up of inductor L, resistance R,
ammeter, battery and switch in series, the current is
greatest at which of the following time intervals, as
measured after the switch is closed?
25% 25% 25% 25%
1.
2.
3.
4.
zero
one time constant
at a time t = L/R
ten time constants
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
A motor with an internal resistance of 10 ohm,
connected to a 24 V battery of negligible resistance,
produces a back emf of 15 V and hence will carry what
current?
25% 25% 25% 25%
1.
2.
3.
4.
3.9 A
2.4 A
1.5 A
0.9 A
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
The self-inductance of a solenoid
increases under which of the following
conditions?
25% 25% 25% 25%
1.
2.
3.
4.
solenoid length is
increased
cross sectional area is
decreased
number of coils per unit
length is decreased
number of coils is
increased
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
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19
20
21
22
23
24
25
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27
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31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
An inductor, battery resistance, and ammeter and
switch are connected in series. If the switch, initially
open, is now closed, what is the current's final value?
1. zero
2. battery voltage
divided by inductance
3. battery voltage times
inductance
4. battery voltage
divided by resistance
25% 25% 25% 25%
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
What is the stored energy in a 0.50
mH coil carrying a current of 4.0 A?
25% 25% 25% 25%
1.
2.
3.
4.
2.0 x 10-3 J
4.0 x 10-3 J
8.0 x 10-3 J
12.0 x 10-3 J
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
In a primary/secondary coil combination, the current in
the secondary is a maximum at the moment that which
one of the following conditions is met in the primary?
1. current is maximum in
positive direction
2. current is maximum in
negative direction
3. rate of current change
is maximum
4. voltage is maximum in
positive direction
25% 25% 25% 25%
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
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31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
A sensitive galvanometer is connected to a wire loop
which is placed within the magnetic field of a strong
horseshoe magnet. The galvanometer shows a
deflection under what conditions?
1.
2.
3.
4.
when the wire is moved
parallel to the field
when the wire is moved
perpendicularly to the
field
when neither wire nor
magnet are moving
when the wire's axis is
parallel to the field
25% 25% 25% 25%
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
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31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
The operation of a tape player to play
music depends on which of the following?
1.
2.
3.
4.
the Doppler effect
the photoelectric effect
the force acting on a
current-carrying wire in a
magnetic field
induced current from the
motion of a magnet past a
wire
25% 25% 25% 25%
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
The operation of an electric motor
depends on which of the following
effects?
1.
2.
3.
4.
25% 25% 25% 25%
the Doppler effect
the photoelectric effect
the force acting on a
current-carrying wire in a
magnetic field
induced current from the
motion of a wire in a
magnetic field
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
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31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
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?
1. enhance the effect
which produces it
2. produce a greater
heating effect
3. produce the greatest
voltage
4. oppose the effect
which produces it
25% 25% 25% 25%
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
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26
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31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
A coil with a self-inductance of 1.5 mH will
show a rate of current change of what
value when inducing an emf of 0.30 V?
25% 25% 25% 25%
1.
2.
3.
4.
200 A/s
0.45 x 10-4 A/s
0.05 A/s
0.30 A/s
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
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48
49
50