15- If pole flux in the DC motor approaches zero, its speed will
(A) approach to infinite
(B) approach to zero
(C) remain constant
(D) approach a stable value between zero and infinite
16- How much voltage regulation will be offered by an ideal DC Generator?
(A) 0
(B) 1
(C) Negative
(D) Infinite
17- Which winding is preferred in d.c. generators to generate large currents?
(A) Lap winding
(B) Fractional winding
(C) Wave winding
(D) Retrogressive wave winding.
18- The efficiency of a d.c. generator is maximum when its variable loss is equal to
(A) The constant loss.
(B) Half of the constant loss.
(C) Double of the constant loss.
(D) One-third of the constant loss.
19- The function of the pole shoes in the case of D.C. machine is to
(A) Spread out the flux to achieve uniform flux density.
(B) Reduce the reluctance of the magnetic path.
(C) Support the field coils
(D) Discharge all the above mentioned functions.
20- The MMF of an interpole is proportional to the
(A) armature current
(B) field current
(C) product of armature current and field current
(D) ratio of armature current to field current
21- DC shunt generators are most suitable for parallel operation due to
(A) identical voltage characteristic
(B) drooping voltage characteristic
(C) rising voltage characteristic
(D) linear voltage characteristic
22- Which of the following DC generator does not need equalizers for satisfactory parallel operation?
(A) Series
(B) Over compound
(C) Flat compound
(D) Under compound
23- The shape of the armature torque (Ta) vs armature current (Ia) characteristic for a DC series motor is a
(A) Parabola from no-load to over-load
(B) Straight line throughout
(C) Parabola from no-load to full-load and straight line at over-load
(D) Parabola throughout
24- Why is DC series motor not started on no-load?
(A) It attains dangerously high speed
(B) It fails to accelerate
(C) It take long time to attain the rated speed
(D) It does not pick up
25- Dummy coils are provided in d.c. generators
(A) To reduce eddy current losses
(B) To amplify voltage
(C) To enhance flux density
(D) To mechanically balance the rotor
26- The speed of a dc shunt motor is
(A) directly proportional to back emf and flux
(B) directly proportional to back emf and inversely proportional to flux
(C) inversely proportional to both back emf and flux
(D) directly proportional to flux and inversely proportional to back emf
27- If a DC series motor is operated on AC supply, it will
(A) spark excessively
(B) have poor efficiency
(C) have poor power factor
(D) all of the above
28- DC series motors are best suited for traction because
(A) torque is proportional to the square of the armature current and speed is proportional to the torque
(B) torque is proportional to the square of the armature current and speed is inversely proportional to the torque
(C) torque and speed both are proportional to the square of the armature current
(D) none of the above
ANSWERS:
15-(A), 16-(A), 17-(A), 18-(A), 19-(D), 20-(A), 21-(B), 22-(D), 23-(C), 24-(A), 25-(D), 26-(B), 27-(D), 28-(B)