In which of the following device the generated emf and armature current are in the opposite directions?
(A) dc generator
(B) dc motor
(C) transformer
(D) all of the above
If the load on a DC shunt motor is increases, its speed is slightly reduced due to______________?
(A) increase in armature current
(B) increase in flux
(C) decrease in reactance
(D) decrease in back emf
The speed of a D.C. shunt motor is required to be more than full load speed. This is possible by______________?
(A) reducing the field current
(B) decreasing the armature current
(C) increasing the armature current
(D) increasing the excitation current
(D) none of the above methods
In the D.C. motor the iron losses occur in____________?
(A) the field
(B) the armature
(C) the brushes
(D) the commutator
Which D.C. motor has got maximum self relieving property ?
(A) Series motor
(B) Shunt motor
(C) Cumulatively compounded motor
(D) Differentially compounded motor
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
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
In a four-pole D.C. machine____________?
(A) all the four poles are north poles
(B) alternate poles are north and south
(C) all the four poles are south poles
(D) two north poles follow two south poles
A separately excited generator as compared to a self-excited generator_____________?
(A) is amenable to better voltage control
(B) is more stable
(C) has exciting current independent of load current
(D) has all above features