## Quiz sheet for efficiency

A windscreen wiper motor is an example of a:

A) permanent magnet motor

B) stepper motor

C) self excited motor

D) brushless motor

ANSWER: A

Brushless dc motors use electronic:

A) commutation

B) current control

C) pulsing

D) voltage

ANSWER: A

The efficiency of a d.c. machine is the ratio of:

A) output power to input power

B) generated e.m.f. to terminal potential difference

C) no load speed to full load speed

D) input power to output power

ANSWER: A

The total copper losses in a d.c. machine are the sum of the:

A) armature and field winding copper losses

B) armature and field voltage drops

C) armature copper losses

D) friction and windage losses

ANSWER: A

To determine the iron loss in a dc machine it is necessary to do a:

A) no load test

B) drop test

C) load test

D) locked rotor test

ANSWER: A

An ideal transformer dissipates

A) zero power

B) unit power

C) infinite power

D) limited power

ANSWER: A

Copper losses in the armature:

A) decrease as load increases

B) are constant at any load

C) decrease proportionally with the armature current

D) decrease proportionally to the armature current squared

ANSWER: D

If a DC motor is driving a 4.8kW load, the electrical power supplied to the motor will be

A) equal to 4.8kW times efficiency

B) equal to 4.8kW minus losses

C) equal to 4.8kW plus efficiency

D) equal to 4.8kW plus losses

ANSWER: D

Maximum efficiency of a motor occurs at.

A) around full load

B) overload

C) very light loads

D) no load

ANSWER: A

The armature is laminated to reduce:

A) eddy current losses in the motor

B) friction and windage loss

C) hysterisis losses in the motor

D) armature reaction loss

ANSWER: A

The field poles of a DC motor:

A) need not be laminated, solid metal may be used

B) must be laminated to reduce armature reaction

C) must be laminated to reduce eddy current loss

D) must be laminated to reduce hysterisis loss

ANSWER: A

The ideal size/shape of the core of an inductor will be:

A) short with a large CSA

B) short with a small CSA

C) long with a large CSA

D) long with a small CSA

ANSWER: A

The iron losses in a DC motor include:

A) hysteresis loss in the armature

B) hysterisis loss in the shunt field

C) power loss due to armature resistance

D) power loss due to shunt field resistance

ANSWER: A

The motor most suited to a load requiring constant speed would be a

A) Shunt connected motor

B) Series connected motor

C) Permanent magnet motor

D) differentially corresponded motor

ANSWER: A

The motor most suited to drive a 9kW load with greatest efficiency would be a

A) 4 kW motor

B) 7 kW motor

C) 10 kW motor

D) 12 kW motor

ANSWER: C

Last modified: Tuesday, 1 June 2021, 9:12 AM