DC Machines Objective Questions Answers

1. The function of brushes in a DC Generator is to:

a) Collect the current from the commutator and supply it to external circuit
b) Prevent the sparking
c) Helps to provide good commutation by offering smooth surface
d) Provide continuity between adjacent commutator segments

A

2. The main advantage of using fractional pitch winding is to reduce:

a) Amount of copper in the winding
b) Size the machine
c) Harmonics in the emf
d) Cost of the machine

A

3. The brushes in dc machine is made of:

a) Aluminium
b) Copper
c) Carbon
d) Mica

C

4. Lap winding is mostly suitable for:

a) Low voltage, high current machines
b) High voltage, high current machines
c) High voltage, low current machines
d) Low voltage, low current machines

A

5. Laminated yoke in dc motor can reduce

a) Temperature rise
b) Iron loss
c) Copper loss
d) Cost of manufacturing

B

6. The thickness of laminations used for armature core of a dc machine is of the order of:

a) 0.005 mm
b) 0.05 mm
c) 0.5 mm
d) 5 mm

C

7. The amount of flux leakage depends on:

a) Air gap length
b) Flux density used in the core and teeth
c) Magnet core shape
d) All the above

D

8. The function of pole shoe in dc machine is:

a) Support the field coils
b) Reduce the reluctance of the magnetic path
c) Spread out the flux to achieve uniform flux distribution in the air gap
d) All the above

D

9. In DC Generator having P number of poles and speed N rpm, the frequency of magnetic reversals will  be:

a) PN/60
b) PN/120
c) PN/240
d) PN/2

A

10. The polarity of the DC Generator is reversed by reversing the direction of the:

a) Rotation
b) Field current
c) Can be either field current and rotation
d) None of the above

B