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1

Lenz's law is a consequence of the fact that energy must be conserved.
A)True
B)False
2

The magnitude of an induced emf is directly proportional to the rate at which magnetic flux lines are cut by a conductor.
A)True
B)False
3

A generator is a device that converts magnetic energy to electric energy.
A)True
B)False
4

A transformer can be used for alternating current only.
A)True
B)False
5

The back emf in the armature of an electric motor is zero when the motor is started and rises as the motor’s speed increases.
A)True
B)False
6

If the armature of a generator is rotating with a constant angular velocity in a constant magnetic field, the induced emf will be constant.
A)True
B)False
7

For an ac generator, the maximum current occurs when the induced emf is a minimum.
A)True
B)False
8

Every motor is also a generator.
A)True
B)False
9

In a shunt-wound motor, the output speed can be controlled by varying the input current to either the field windings or the armature windings.
A)True
B)False
10

A series-wound motor is preferable if a large starting torque is desirable.
A)True
B)False
11

When a wire moves perpendicular to a magnetic field, the induced emf does not depend on the
A)velocity of the wire
B)resistance of the wire
C)flux density of the magnetic field
D)orientation of the wire
12

A wire parallel to the paper moves downward into a flux density directed into the paper. The induced current will be
A)directed to the left
B)zero because the motion is perpendicular to the field
C)directed to the right
D)opposite to the induced emf, according to Lenz's law
13

Which of the following is not a component of a simple ac generator?
A)Field magnet
B)Split-ring commutator
C)Armature
D)Brushes
14

The instantaneous emf produced by a simple ac generator is a maximum when the angular displacement of the loop is an
A)integral multiple of π/2
B)odd multiple of π/2
C)even multiple of π
D)odd multiple of π
15

A coil of wire of area 0.3 m2 has 90 turns of wire and is suspended with its plane perpendicular to a uniform magnetic field. An emf of -2 V is induced when the coil is flipped parallel to the field in 0.4 s. The flux density of the field is approximately
A)0.01 T
B)0.02 T
C)0.03 T
D)0.04 T
16

An armature in an ac generator consists of 600 turns, each having an area of 0.4 m2. The coil rotates in a field of flux density 2 x 10-3 T. What must the rotational frequency of the armature be to induce a maximum emf of 12 V?
A)200 rpm
B)226 rpm
C)239 rpm
D)478 rpm
17

A wire 0.2 m long moves at a constant speed of 5 m/s in a direction that is 37° with respect to a magnetic field of 0.2 T directed perpendicular to the wire. The induced emf is approximately
A)0.12 V
B)0.16 V
C)0.20 V
D)0.24 V
18

A 120-V shunt motor has a field resistance of 200 Ω and an armature resistance of 12 Ω. At full speed, the back emf of the motor is 90 V. The operating current is approximately
A)3 A
B)6 A
C)12 A
D)16 A
19

A transformer has 400 secondary turns and only 50 primary turns. If an ac voltage of 120 V is connected to the primary coil, the output voltage is
A)15 V
B)240 V
C)430 V
D)960 V
20

A magnetic flux changing at the rate of one will induce an emf of one for each of the conductor.
21

For a dc motor in operation, the net voltage delivered to the armature coils is equal to the less the .
22

The major components of a simple ac generator are the , , and with .
23

Three types of motors discussed in this text are the , , and .
24

The current drawn by an electric motor is a maximum when the motor is .
25

If an ideal transformer, the power output is equal to the .
26

In a step-down transformer, the number of turns in the secondary coil must be the number of turns in the primary coil.
27

A simple transformer consists of three essential parts: , , and .
28

In a(n) , the field windings and the armature windings are connected in parallel.







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