141. In dc machines , the armature reaction mmf is
a) stationary with respect to armature
b) rotating with respect to stator
c) stationary with respect to stator
d) rotating with respect to brushes.
ans. c
142. The purpose of using interpoles in dc machines is to nullify
a) the demagnetising effect of armature mmf
b) the cross magnetising effect of armature mmf
c) the reactance voltage
d) both the cross-magnetizing mmf and the reactance voltage
ans. d
143. In dc generators, the polarity of interpoles is
a) same as that of main pole behind
b) same as that of mail pole ahead
c) opposite to that of the mail pole
d) none of these
ans. b
144. The object of using compensation winding in dc machines is to neutralize the
a) armature reaction in the interpolar zone
b) armature reaction in the commutating zone
c) armature reaction under the pole faces
d) cross-magnetizing armature reaction.
ans. c
145. The emf generated in a dc generator is
a) dynamically induced emf
b) statically induced emf
c) electrostatically induced emf
d) magnetically induced emf
ans. a
146. The yoke of generator is made of cast iron because
a) it is cheaper
b) it completes the magnetic path
c) it gives mechanical protection to the machine
d) all of these
ans. d
147. The field of self excited generator is excited by
a) dc
b) ac
c) its own current
d) ac and dc both
ans. c
148. The DC generator works on the principle of
a) Faraday's laws of electron magnetic induction
b) lenz's law
c) the current carrying conductor placed in the magnetic field an emf is produced .
d) induction.
ans. a
149. The carbon brushes are generally used as they
a) are self lubricating
b) are soft
c) have negative temperature coefficient
d) possess all the above three properties
ans. d
150. Armatures are made of laminated steel instead wood because it has
a) low permeability
b) high permeability
c) more mechanical strength
d) more mechanical strength and high permeability
a) stationary with respect to armature
b) rotating with respect to stator
c) stationary with respect to stator
d) rotating with respect to brushes.
ans. c
142. The purpose of using interpoles in dc machines is to nullify
a) the demagnetising effect of armature mmf
b) the cross magnetising effect of armature mmf
c) the reactance voltage
d) both the cross-magnetizing mmf and the reactance voltage
ans. d
143. In dc generators, the polarity of interpoles is
a) same as that of main pole behind
b) same as that of mail pole ahead
c) opposite to that of the mail pole
d) none of these
ans. b
144. The object of using compensation winding in dc machines is to neutralize the
a) armature reaction in the interpolar zone
b) armature reaction in the commutating zone
c) armature reaction under the pole faces
d) cross-magnetizing armature reaction.
ans. c
145. The emf generated in a dc generator is
a) dynamically induced emf
b) statically induced emf
c) electrostatically induced emf
d) magnetically induced emf
ans. a
146. The yoke of generator is made of cast iron because
a) it is cheaper
b) it completes the magnetic path
c) it gives mechanical protection to the machine
d) all of these
ans. d
147. The field of self excited generator is excited by
a) dc
b) ac
c) its own current
d) ac and dc both
ans. c
148. The DC generator works on the principle of
a) Faraday's laws of electron magnetic induction
b) lenz's law
c) the current carrying conductor placed in the magnetic field an emf is produced .
d) induction.
ans. a
149. The carbon brushes are generally used as they
a) are self lubricating
b) are soft
c) have negative temperature coefficient
d) possess all the above three properties
ans. d
150. Armatures are made of laminated steel instead wood because it has
a) low permeability
b) high permeability
c) more mechanical strength
d) more mechanical strength and high permeability
