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
Related Mcqs:
- If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be________________?
A. demagnetisation only
B. cross magnetisation as well as mag¬netisation
C. crossmagnetisation as well as demagnetising
D. cross magnetisation only - In lap winding, the number of brushes is always_____________?
A. double the number of poles
B. same as the number of poles
C. half the number of poles
D. two - Brushes of D.C. machines are made of_________?
A. carbon
B. soft copper
C. hard copper
D. all of above - The material for commutator brushes is generally_______________?
A. mica
B. copper
C. cast iron
D. carbon - In D.C. generators, the brushes on commutator remain in contact with conductors which_________________?
A. lie under south pole
B. lie under north pole
C. lie under interpolar region
D. are farthest from the poles - To achieve sparkless commutation brushes of a D.C. generator are rockedm ahead so as to bring them?
A. just ahead of magnetic neutral axis
B. in magnetic neutral axis
C. just behind the magnetic neutral axis
D. none - Armature coil is short circuited by brushes when it lies_____________?
A. along neutral axis
B. along field axis
C. in any of the above positions
D. in none of the above positions - The rapid wear of brushes takes place due to____________?
A. abrasion from dust
B. excessive spring pressure
C. rough commutator bars
D. high mica insulation between com-mutation bars
E. all of the above factors - The number of brushes in a commutator depends on______________?
A. speed of armature
B. type of winding
C. voltage
D. amount of current to be collected - In a D.C. generator in order to reduce sparking at brushes, the self-induced e.m.f. in the coil is neutralised by all of the following except______________?
A. interpoles
B. dummy coils
C. compensating winding
D. shifting of axis of brushes
