DC Machines MCQ Objectives

1. In a separately excited dc generator the field is connected to:

a) In series with an armature

b) Across the armature

c) To the external supply source

d) None of the above

C

2. If we increase the field of the dc generator, its emf output:

a) Increases indefinitely

b) Increases till the winding burns

c) Increases till the magnetic saturation takes place

d) First increases and then starts reducing

C

3. In a dc generator the residual magnetism is of the order of:

a) 2.5%

b) 10%

c) 15%

d) 25%

A

4. The terminal voltage of the dc shunt generator on loading:

a) Increases slightly

b) Decreases sharply

c) Decreases slightly

d) Increases sharply 

C

5. For parallel operation, the dc shunt generator normally preferred are:

a) Shunt generator

b) Series generator

c) Under compound generator

d) Both (a) and (c)

D

6. In a rotating electrical machine the torque produced will be maximum when:

a) Torque angle is zero

b) Torque angle is 90 deg

c) Two magnetic fields are aligned with each other

d) Field strengths are maximum and the torque angle is zero

B

7. Flashing of field of dc generator means:

a) Neutralization of residual magnetism

b) Creation  of the residual magnetism by a dc source

c) Increasing the flux density by providing extra ampere-turns in the field

d) None of the above

B

8. In an arc welding in order to obtain steady arc one should use:

a) DC series generator

b) DC shunt generator

c) DC differential compound generator

d) DC cumulative compound generator

C

9. With the increase in the speed of a dc motor:

a) Both back emf as well as line current increases

b) Both back emf and line current falls

c) Back emf increases but the line current falls

d) Back emf falls and line current increases

C

10. The output indicated on the name plate of any motor is always the:

a) Gross power

b) Power drawn in volt amperes

c) Power drawn in watts

d) Output power at the shaft

D

11. In a dc compound motor field regulator is provided to:

a) Control the flux

b) Limit the ampere current

c) Demagnetize the field partially

d) None of the above

A

12. The direction of rotation of dc shunt motor can be reversed by interchanging:

a) The supply terminals

b) The field terminals

c) The armature terminals only

d) Either field or armature terminals

D