2ND 7

Question 1

Commutator segments are insulated from each other by:

a) small strips of wood
b) a rubber insert
c) laminated varnish
d) sheet mica

Answer 1

d) sheet mica

Question 2

Most DC generator brushes that carry the current from the commutator to the external circuit are made of:

a) carbon and lead
b) carbon and graphite
c) graphite and lead
d) copper and lead

Answer 2

b) carbon and graphite

Question 3

The degree that the neutral plane of a DC generator will shift under load is:

a) inversely proportional to the load
b) proportional to the load
c) always less than proportional to the load
d) independent of the load

Answer 3

b) proportional to the load

Question 4

DC generators are generally classified according to the manner in which:

a) they are used
b) the field windings are connected to the load
c) the armature circuit is connected to the load
d) the field windings are connected to the armature circuit

Answer 4

d) the field windings are connected to the armature circuit

Question 5

The effects of armature reaction in a DC generator are reduced by the use of:

a) commutating windings
b) commutating windings and interpoles
c) commutating or interpoles
d) exciter current

Answer 5

c) commutating or interpoles

Question 6

A shunt wound DC generator will build up to full terminal voltage with no external load connected to it due to:

a) the large conductors used in the armature
b) motor action of the generator
c) interpoles
d) self-excitation

Answer 6

d) self-excitation

Question 7

The part of a DC generator into which the working voltage is induced is the:

a) yoke
b) field poles
c) armature
d) commutator

Answer 7

c) armature

Question 8

The field coil windings of a self-excited DC generator are:

a) series
b) shunt
c) compound
d) any one of the above

Answer 8

d) any one of the above

Question 9

The rated voltage value of a DC generator will be reached faster if the generator is:

a) separately excited
b) self-excited
c) brought up to speed rapidly
d) none are correct

Answer 9

b) self-excited

Question 10

A shunt most nearly means a:

a) parallel circuit
b) series circuit
c) series-parallel circuit
d) any of the above

Answer 10

a) parallel circuit

Question 11

Which of the following is true regarding the speed regulation of a shunt motor?

a) it has a constant speed characteristic under varying loads
b) it has a varying speed characteristic under varying loads
c) it has a varying speed characteristic under constant loads
d) none of the above are correct

Answer 11

a) it has a constant speed characteristic under varying loads

Question 12

A DC series motor is more adaptable where a:

a) small variation of torque and speed is needed
b) wide variation of torque but a small variation of speed is needed
c) wide variation of torque is required and wide variations in speed are allowable
d) constant speed is needed

Answer 12

c) wide variation of torque is required and wide variations in speed are allowable

Question 13

When the load is applied to a DC shunt motor, which one of the following will happen?

a) speed decreases – counter EMF goes up
b) speed increases – counter EMF goes down
c) speed increases – counter EMF goes up
d) speed decreases – counter EMF goes down

Answer 13

d) speed decreases – counter EMF goes down

Question 14

The counter EMF of a DC motor is zero when the:

a) motor is at rated speed
b) armature is not turning
c) motor is almost up to rated speed
d) armature has just begun to turn

Answer 14

b) armature is not turning

Question 15

The horsepower developed by a motor depends mainly upon which of the following two factors:

a) speed and voltage
b) speed and torque
c) torque and voltage
d) torque and watts

Answer 15

b) speed and torque

Question 16

A motor which has an output of 820 watts and an input of 960 watts has an efficiency of appraximately:

a) 90%
b) 85%
c) 75%
d) 70%

Answer 16

b) 85%

Question 17

If the no-load speed of a shunt motor is 1800 rpm and the full-load speed is 1475 rpm, the speed regulation is:

a) 18%
b) 22%
c) 2.2%
d) 1.8%

Answer 17

b) 22%

Question 18

The generated voltage (counter EMF) of a motor:

a) opposes the impressed voltage
b) opposes any change in load
c) aids the impressed voltage
d) none of the above are correct

Answer 18

a) opposes the impressed voltage

Question 19

Too much resistance inserted in the field circuit of a shunt or compound motor will:

a) cause the motor to slow down
b) increase back voltage
c) allow the motor to overspeed and destroy itself
d) not affect the motor

Answer 19

c) allow the motor to overspeed and destroy itself

Question 20

The main purpose of the commutator on a DC motor is to:

a) convert DC voltage to AC
b) prevent the armature polarity from automatically reversing itself as the brushes move from one segment to another
c) automatically reverse the polarity of the field coils
d) automatically reverse the armature polarity each time the brushes move from one segment to another

Answer 20

d) automatically reverse the armature polarity each time the brushes move from one segment to another