In a commutator_____________?

A. Copper is harder than mica
B. Mica and copper are equally hard
C. Mica is harder than copper
D. None of the above

According to Fleming’s right-hand rule for finding the direction of induced e.m.f., when middle finger points in the direction of induced e.m.f., forefinger will point in the direction of____________?

A. Motion of conductor
B. Lines of force
C. Either of the above
D. None of the above

While applying Fleming’s right-hand rule to And the direction of induced e.m.f., the thumb points towards___________?

A. Direction of induced e.m.f.
B. Direction of flux
C. Direction of motion of the conductor if forefinger points in the direction of generated e.m.f.
D. Direction of motion of conductor, if forefinger points along the lines of flux

In D.C. generators the pole shoes are fastened to the pole core by_____________?

A. Rivets
B. Counter sunk screws
C. Brazing
D. Welding

Fleming’s right-hand rule regarding direction of induced e.m.f., correlates__________?

A. Magnetic flux, direction of current flow and resultant force
B. Magnetic flux, direction of motion and the direction of e.m.f. induced
C. Magnetic field strength, induced voltage and current
D. Magnetic flux, direction of force and direction of motion of conductor

In case of D.C. machines, mechanical losses are primary function of____________?

A. Current
B. Voltage
C. Speed
D. None of above

Copper brushes in D.C. machine are used_____________?

A. Where low voltage and high currents are involved
B. Where high voltage and small cur-rents are involved
C. In both of the above cases
D. In none of the above cases

For a D.C. generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher e.m.f___________ ?

A. Lap winding
B. Wave winding
C. Either of a. and b. above
D. Depends on other features of design

In D.C. generators, the cause of rapid brush wear may be___________?

A. Severe sparking
B. Rough commutator surface
C. Imperfect contact
D. Any of the above

The bearings used to support the rotor shafts are generally______________?

A. Ball bearings
B. Bush bearings
C. Magnetic bearmgs
D. Needle bearings