Description : The insulating material used between the commutator segments is normally (a) graphite (b) paper (c) mica (d) insulating varnish
Last Answer : Ans: c
Description : The material for commutator brushes is generally (a) mica (b) copper (c) cast iron (d) carbon
Last Answer : Ans: d
Description : Brushes of D.C. machines are made of (a) carbon (b) soft copper (c) hard copper (d) all of above
Last Answer : Ans: a
Description : In D.C. generators, current to the external circuit from armature is given through (a) commutator (b) solid connection (c) slip rings (d) none of above
Description : Iron losses in a D.C. machine are independent of variations in (a) speed (b) load (c) voltage (d) speed and voltage
Last Answer : Ans: b
Description : In case of D.C. machines, mechanical losses are primary function of (a) current (b) voltage (c) speed (d) none of above
Description : A separately excited generator as compared to a self-excited generator (a) is amenable to better voltage con-trol (b) is more stable (c) has exciting current independent of load current (d) has all above features
Description : 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
Description : 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
Description : 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
Description : 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