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
If B is the flux density, I the length of conductor and v the velocity of conductor, then induced e.m.f. is given by______________?
(A) Blv
(B) Blv2
(C) Bl2v
(D) Bl2v2
If a D.C. generator fails to build up the probable cause could not be_____________?
(A) imperfect brush contact
(B) field resistance less than the critical resistance
(C) no residual magnetism in the generator
(D) faulty shunt connections tending to reduce the residual magnetism
Brushes of D.C. machines are made of_________?
(A) carbon
(B) soft copper
(C) hard copper
(D) all of above
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
Iron losses in a D.C. machine are independent of variations in______________?
(A) speed
(B) load
(C) voltage
(D) speed and voltage
Iron losses in a D.C. machine are independent of variations in_____________?
(A) speed
(B) load
(C) voltage
(D) speed and voltage