Deck 21: DC Motors

Question 1

Not all electric motors are suited to have their speed controlled with smooth acceleration or deceleration, but DC motors do have this ability.

Answer 1

True

Question 2

A compound motor can be obtained by placing both a series field winding and a shunt field winding on the field poles of the motor.

Answer 2

True

Question 3

Motors and generators are look-alikes with their armature, field poles, commutators, and such, and where they differ is in the opposite application of electromagnetism.

Answer 3

True

Question 4

Every motor inadvertently acts like a generator and produces a voltage known as ____ (cemf) within itself while it is running.

A)center-emf
B)counter-emf
C)controlled emf
D)categorical emf

Question 5

Wave windings require only four parallel paths through the armature in one complete wave winding, regardless of the number of brushes.

Question 6

The maximum torque obtainable from a DC motor is limited by commutation rather than by ____.

A)speed
B)rotation
C)heating
D)flux

Question 7

In general, lap windings require as many brushes as there are ____ and as many parallel paths through the armature as there are poles.

A)poles
B)coils
C)filaments
D)drums

Question 8

DC motors, like ____, are classified by the way their field coils are connected; thus, we differentiate between shunt motors, series motors, and compound motors.

A)AC motors
B)AC generators
C)DC generators
D)torque motors

Question 9

When the torque increases to meet the new load demand, the speed will readjust itself; thus, the motor maintains a fairly constant speed.

Question 10

To counteract the warping of the magnetic field, large AC motors are often built with interpoles, or commutating poles.

Question 11

Unlike the shunt-motor field in which magnetization is attained by a small current in many turns, the series-motor field carries the entire current in a ____ coil of few turns.

A)no-resistance
B)low-resistance
C)medium-resistance
D)high-resistance

Question 12

The cadmium-controlled rectifier (CCR) is the most popular device among the thyristors, or electronic switches.

Question 13

Compound motors are generally connected long shunt and are called cumulative ____ motors.

A)compound
B)torque
C)speed
D)ratio

Question 14

In the brush-type PM motor, the armature winding is no longer rotating, but is mounted within the outer frame structure, and is now called the stator.

Question 15

The practical and preferred way to vary the speed of a DC motor is by varying the ____ in the shunt field circuit.

A)rotation
B)pressure
C)current
D)resistance

Question 16

The generated emf is a measure of the useful mechanical energy obtained from the neutrons passing through the armature.

Question 17

Lap windings are good for high-current, low-voltage motors, and wave windings are good for ____ motors and generators.

A)high-voltage, high-current
B)low-voltage, low-current
C)high-voltage, low-current
D)low-voltage, high-current

Question 18

The ____ motor has become a favorite in high-technology applications involving motion control, such as robotics.

A)shunt
B)series
C)compound
D)permanent-magnet

Question 19

The direction of rotation of a DC motor can be reversed by changing the connections of either the armature or the field leads.

Question 20

Brushless PM motors have become very popular for ____ applications such as air handlers found in the air-conditioning field.

A)variable-speed
B)increased-speed
C)low-speed
D)reduced-speed