136. In a D.C. generator the critical resistance can be
increased by
(A) increasing its field resistance
(B) decreasing its field resistance
(C) increasing its speed
(D) decreasing its speed
Ans: C
137. For a D.C. machines laboratory following type of D.C.
supply will be suitable
(A) rotary converter
(B) mercury are rectifier
(C) induction motor D.C. generator set
(D) synchronous motor D.C. generator set
Ans: C
138. The function of pole shoes in the case of D.C. machine
is
(A) to reduce the reluctance of the
magnetic path
(B) to spread out the flux to achieve
uniform flux density
(C) to support the field coil
(D) to discharge all the above functions
Ans: D
139. In the case of lap winding resultant pitch is
(A) multiplication of front and back
pitches
(B) division of front pitch by back pitch
(C) sum of front and back pitches
(D) difference of front and back pitches
Ans: D
140. A D.C. welding generator has
(A) lap winding
(B)
wave moving
(C) duplex winding
(D) any of the above
Ans: A
141. Which of the following statement about D.C. generators
is false ?
(A) Compensating winding in a D.C.
machine helps in commutation
(B) In a D. C. generator inter-poles
winding is connected in series with the armature winding
(C) Back pitch and front pitch are both
odd and approximately equal to the pole pitch
(D) Equilizing bus bars are used with
parallel running of D.C. shunt generators
Ans: D
142. The demagnetising component of armature reaction in a
D.C. generator
(A) reduces generator e.m.f.
(B) increases armature speed
(C) reduces interpoles flux density
(D) results in sparking trouble
Ans: A
143. Magnetic field in a D.C. generator is produced by
(A)
electromagnets
(B) permanent magnets
(C) both (A) and (B)
(D) none of the above
Ans: A
144. 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
Ans: D
145. Compensating windings are used in D.C. generators
(A) mainly to reduce the eddy currents by
providing local short-circuits
(B) to provide path for the circulation
of cooling air
(C) to neutralise the cross-magnetising
effect of the armature reaction
(D) none of the above
Ans: C
146. Differentially compound D.C. motors can find
applications requiring
(A) high starting torque
(B) low starting torque
(C) variable speed
(D) frequent on-off cycles
Ans: B
147. Which D.C. motor is preferred for elevators ?
(A) Shunt motor
(B) Series motor
(C) Differential compound motor
(D) Cumulative compound motor
Ans: D
148. According to Fleming's left-hand rule, when the
forefinger points in the direction of the field or flux, the middle finger will
point in the direction of
(A) current in the conductor
(B) rotation of conductor
(C) resultant force on conductor
(D) none of the above
Ans: A
149. If the field of a D.C. shunt motor gets opened while
motor is running
(A) the speed of motor will be reduced %
(B) the armature current will reduce
(C) the motor will attain dangerously
high speed 1
(D) the motor will continue to nuvat
constant speed
Ans: C
150. Starters are used with D.C. motors because
(A) these motors have high starting
torque
(B) these motors are not self-starting
(C) back e.m.f. of these motors is zero
initially
(D) to restrict armature current as there
is no back e.m.f. while starting
