(a) demagnetisation of leading pole tip and magnetisation of trailing pole tip (b) demagnetisation of trailing pole tip and magnetisation of leading pole tip (c) damagnetising the center of all poles
(d) magnetising the center of all poles
Answer: a
Ques 24. The critical resistance of the D.C. generator is the resistance of (a) field
(b) brushes (c) armature (d) load
Answer: a
Ques 25. The terminal voltage of a series generator is 150 V when the load current is 5 A. If the load current is increased to 10 A, the terminal voltage will be
(a) 150 V
(b) less than 150 V (c) greater than 150 V (d) none of the above
Answer: c
Ques 26. The open circuit voltage of a compound generator is 250 V. At full load the terminal voltage (a) will be less than 250 V
(b) will always be 250 V
(c) may be greater or less than 250 V (d) none of the above
Answer: c
Ques 27. 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
Answer: c
Ques 28. The direction of rotation of a D.C. series motor can be changed by (a) interchanging supply terminals
(b) interchanging field terminals (c) either of (a) and (b) above (d) None of the above
Answer: b
Ques 29. Which D.C. motor will be preferred for machine tools ? (a) Series motor
(b) Shunt motor
(c) Cumulative compound motor (d) Differential compound motor
Answer: b
Ques 30. 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
Answer: d
Ques 31. Main advantage of DC motor is a. It is cheap
b. It provides fine speed control c. It is simple in construction d. It has no replacement Answer: b
Ques 32. In D.C. shunt motors as load is reduced (a) the speed will increase abruptly
(b) the speed will increase in proportion to reduction in load (c) the speed will remain almost/constant
(d) the speed will reduce Answer: c
Ques 33. If a D.C. motor is connected across the A.C. supply it will (a) run at normal speed
(b) not run
(c) run at lower speed
(d) burn due to heat produced in the field winding by .eddy currents
Answer: d
Ques 34. The back EMF in a DC motor a. Opposes the applied voltage b. Aids the armature current c. Aids the supplied voltage d. Opposes the armature current Answer: a
Ques 35. Back EMF in a DC motor is maximum at a. No load
b. Half full load c. Full load d. ¾ full load Answer: a
Ques 36. A motor takes a large current at starting because a. The armature resistance is high
b. Beck EMF is low c. Back EMF is high
d. Shunt filed is producing weak field Answer: b
Ques 37. When the speed of a DC motor increases, its armature current a. Increases
b. Remains same c. Decreases d. Becomes infinite
Answer: c
Ques 38. The armature of a DC machine is made of a. Silicon steel
b. Cast steel c. Wrought iron d. Soft iron Answer: c
Ques 39. The armature of a DC machine is laminated in order to reduce a. Eddy current loss
b. Copper loss c. Hysteresis loss d. Frictional loss Answer: a
Ques 40. A series motor will over speed when a. The load is increased
b. The armature circuit is open c. The field is opened
d. Load is removed Answer: d
Ques 41. What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?
(a) The motor will stop
(b) The motor will continue to run (c) The armature may burn (d) The motor will run noisy
Answer: c
Ques 42. In case of D.C. shunt motors the speed is dependent on back e.m.f. only because (a) back e.m.f. is equal to armature drop
(b) armature drop is negligible
(c) flux is proportional to armature current
(d) flux is practically constant in D:C. shunt motors
Answer: d
Ques 43. By looking at which part of the motor, it can be easily confirmed that a particular motor is D.C.
motor?
(a) Frame (b) Shaft (c) Commutator (d) Stator
Answer: c
Ques 44. The starting resistance of a D.C. motor is generally (a) low
(b) around 500 Q (c) 1000 Q (d) infinitely large
Answer: a
Ques 45. The speed of a D.C. series motor is (a) proportional to the armature current
(b) proportional to the square of the armature current (c) proportional to field current
(d) inversely proportional to the armature current
Answer: d
Ques 1. A transformer will work on a. AC only
b. AC as well as DC c. DC only
d. Pulsating DC Answer: a
Ques 2. When the primary of a transformer is connected to a DC supply a. The primary draws small current
Transformers and Induction Motors:
b. Primary reactance is increased c. Core losses are increased d. Primary may burn out Answer: d
Ques 3. A transformer will have zero efficiency at a. Full load
b. Half load c. No load
d. Twice the full load Answer: c
Ques 4. The voltage per turn of the primary of a transformer is……….the voltage per turn of the secondary
a. More than b. Same as c. Less than d. Twice Answer: b
Ques 5. The winding of the transformer with greater number of turns will be a. High voltage winding
b. Low voltage winding
c. Either high or low voltage winding d. High power
Answer: a
Ques 6. The number of parallel paths in a simplex lap winding is equal to a. 2
b. Number of poles c. Number of pair poles d. 1
Answer: b
Ques 7. In a simplex wave winding the number of parallel paths is equal to a. Number of poles
b. 2
c. Number of pair poles d. 1
Answer: b
Ques 8. In a lap winding, the number of brushes required are equal to a. Number of poles
b. Commutator pitch c. Number of pair of poles d. Number of coils
Answer: a
Ques 9. For the same rating, a DC machine has……….an AC machine a. The same as
b. Less weight than c. More weight than d. Half the weight than Answer: c
Ques 10. If the capacitor of a single‐phase motor is short‐circuited (a) the motor will not start
(b) the motor will run
(c) the motor will run in reverse direction
(d) the motor will run in the same direction at reduced r.p.m.
Answer: a
Ques 11. The running winding of a single phase motor on testing with meggar is found to be ground. Most probable location of the ground will be
(a) at the end connections (b) at the end terminals
(c) anywhere on the winding inside a slot
(d) at the slot edge where coil enters or comes out of the slot
Answer: d
Ques 12. Direction of rotation of a split phase motor can be reversed by reversing the connection of