Worksheets3.12 Cat B
Total questions: 16
Worksheet time: 8mins
Name
Class
Date
1.
What is the advantage of a series field motor?
a)
Its RPM is very stable, even with load changes.
b)
It has the highest starting torque of all electric motors.
c)
It doesn't need brushes and slip rings.
d)
It has the greatest Voltage drop over the field windings of all electric motors
2.
What is the advantage of a shunt field motor?
a)
Its RPM is very stable, even with load changes.
b)
It has the highest starting moment of all electric motors.
c)
It doesn't need brushes and slip rings.
d)
It has the highest current draw through the field windings of all electric motors
3.
Which type of motor is suitable for use as a starter?
a)
Series field motor
b)
Shunt field motor
c)
Asynchronous motor
d)
Parallel wound induction motor
4.
What is the purpose of the excitation winding in a DC machine?
a)
To generate a static magnetic field in the stator.
b)
To generate a static magnetic field in the rotor.
c)
To increase the output power.
d)
To generate a Rotating Magnetic Field (RMF) in the stator
5.
How is the rotation direction of a DC machine changed?
a)
By interchanging the supply leads.
b)
By reversing the current direction in the armature winding or the excitation winding.
c)
By reversing the current direction in the stator winding.
d)
By increasing the frequency of the supply voltage
6.
Why are interpoles fitted to the main poles of DC machines?
a)
To increase the flux density of the field.
b)
To boost the field strength.
c)
To counter the effects of armature reaction on the main field.
d)
To create a rotating magnetic field in the stator
7.
Which part provides the power supply for the armature in a DC machine?
a)
Excitation winding
b)
Pole shoe
c)
Commutator
d)
The rotating rectifying diode pack.
8.
What is the purpose of the commutator in a DC motor?
a)
To generate a stationary magnetic field into the motor.
b)
To energise the coil at the appropriate time in the revolution of the motor.
c)
To generate a rotating magnetic field into the motor.
d)
To reduce the resistance in the armature windings
9.
How is the excitation winding and the armature winding connected in a Shunt Wound DC Motor?
a)
Series
b)
Crossed
c)
Intermittent
d)
Parallel
e)
Series-parallel
10.
What is the effect on the armature cross-field with an increase in armature current in a DC motor?
a)
The cross-field is weakened.
b)
The cross-field is strengthened.
c)
The cross-field is not influenced.
d)
The cross-field reverses.
11.
What is armature reaction?
a)
The impact of the armature cross-field on the main field.
b)
The back EMF produced in the armature.
c)
The reaction to the torque produced by the stator.
d)
Impact of the resistive force of the load on the armature angle with reference tot he main field
12.
What is the cause of reactive sparking?
a)
The meeting of the coils and brushes within the neutral zone.
b)
The meeting of the coils and brushes outside the neutral zone.
c)
The positioning of the brushes on the magnetic neutral axis.
d)
Poor contact of the bushes with the commutator
13.
Where are compensating windings located in DC machines?
a)
In parallel with the interpoles
b)
On the commutator
c)
Within the main poles
d)
Within the armature windings
14.
Which two methods may be employed for speed control of DC machines?
a)
Current control and reactance control
b)
Voltage control and inductance control
c)
Voltage control and field control
15.
What is an advantage of a shunt-wound DC motor?
a)
It doesn't need brushes and a slip ring.
b)
It has a very high starting torque.
c)
It has a constant speed at various loads.
d)
It is easy to control the speed by varying the voltage over the field windings
16.
What is the purpose of the commutator in a DC motor?
a)
It is used as a switch to control field strength in the stator.
b)
It is used as a switch to reverse the polarity of the power supply to the stator.
c)
It is used as a switch to reverse the polarity of the power supply to the armature.
100 %
