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Electrical Circuits & Machines SPPU MCQ Full Paper With Answers 2020





Electrical Circuits  & Machines SPPU MCQ Full Paper With Answers 2020. This all questions and answers are asked in SPPU exam paper online 2020.

1. The field winding of three phase synchronous machine is excited by

                a. 1 phase ac supply

                b. 3 phase ac supply

                c. DC supply

                d. Supply obtained from an inverter

                Ans - b

 

2. The primary & secondary induced EMF's E1 and E2 in a two winding x'mer ( Transformer ) are always

                a. Equal in magnitude

                b. Anti-phase with each other

                c. Anti-phase with each other

                d. Determined by nature of load on secondary

                Ans - C

 

3. The field of an induction motor rotates relatives to the stator of

                a. rotor speed

                b. Slip speed

                c. Synchronous speed

                d. Very low speed

                Ans - c

 

4. In BLDC, motor if load increases, speed of motor----

                a. increases

                b. decre.

                c. remains same

                d. none of above

                Ans - B

 

5. If the Thevenin equivalent ckt of network has Vth= 10V & Rth=10ohm, the maximum power trasferred by the network to the load is

                a. 5W

                b. 10W

                c. 2.5 W

                d. 7.5W

                Ans – C

 

6. A 12 mA current source has an internal resistance RS of 1.2k, The equivalent voltage source is---

                a. 144v

                b. 14.4v

                c. 7.2v

                d. 72mv

                Ans – B

 

7. Number of different speed that can be obtained from two induction motors in cascade is

                a. 6

                b. 4

                c. 3

                d. 2

                Ans –b

 

8. A stepper motor may be considered as a --- converter.

                a. Ac to dc

                b. dc to ac

                c. dc to dc

                d. Digital to analog

                Ans - a

9. One method of neutralizing the armature reaction in a dc generator is to

                a. Shift the brushes in lagging direction of rotation

                b. Shift the brushes in leading direction of rotation

                c. Interchange the terminals at the brushes

                d. None

                Ans – b

 

10. A pole, 50Hz, 3 phase induction motor runs at the speed of 1440 rpm. The frequency of induced emf is ---

                a. 3hz

                b. 2.5 hz

                c. 2hz

                d. 1.5hz

                Ans –

 

11. Starters are used in induction motor because

                a. Its starting torque is high

                b. its is run against heavy load

                c. it cannot run in reverse direction

                d. its starting current is five times or more than its rated current

                Ans –

 

12. In a transformer the resistance between its primary and secodary should be

                a. zero

                b. 100Q

                c. 10Q

                d. infinity

                Ans – d

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13. In superposition theorm, while considering a source, all other current sources are

                a. Short circuited

                b. change its position

                c. open circuited

                d. removed from the circuit

                Ans – c

 

14. The terminal voltage of dc shunt generator drpos on load because of

                a. armature reaction

                b. armature resistance

                c. weakemimg of the field due to armature reaction

                d. all

                Ans – d

 

15. Which of the following is true about an ideal voltage source

                a. 0 resistance

                b. small emf

                c. large emf

                d. infinite resistance

                Ans – a

 

16. In an induction motor, rotor slots are usually not quite parallel to the shaft are given a slight skew

                a. to reduce the magnetic hum

                b. to reduce the locking tendency of rotor

                c. both a & b

                d. to increase the speed of the motor

                Ans - a

17. The rotor speed of 6 pole 50 hz induction motor is 960 rpm. The percentage slip is ---

                a. 03

                b. 04

                c. 05

                d. 0.1

Ans –

 

18. The rotor speed is more than the synchronous speed in 3 phase induction motor, when ---

                a. slip is +ve

                b. slip is -ve

                c. slip is 0

                d. slip is 1

                Ans -      a

19. For 4 pole 50hz, induction motor, the full load slip is 0.03. Hence its full load speed is --- rpm

                a. 1420

                b. 1455

                c. 1495

                d. 1500

                Ans –

 

20. Windings are made with ---

                a. Al

                b. Cu

                c. Both a & b

                d. Fu

                Ans – c

 

21. In dc machines, armature windings are placed on the rotor beacause of the necessity for

                a. Electromechanical energy converter

                b. generation of voltage

                c. commutation

                d. development of torque

                Ans - a

22. The norton equivalent current is --

                a. the current through the load

                b. the open current from the source

                c. the short ckt current

                d. none

                Ans – c

 

23. Superposition thoerm is not applicable for

                a. volt. of calculation

                b. bilateral calculation

                c. power calculation

                d. passive elements

                Ans – c

 

24. What will happen, with the increase in speed of a DC motor

                a. Back emf increases but line current fails

                b. Back emf falls and line current incre.

                c. Both Back emf as well as line current incre.

                d. Both Back emf as well as line current fails

                Ans – a

 

25. The no. of poles in 3 phase induction motor is determined by the ---

                a. supply freq.

                b. motor speed

                c. supply volt.

                d. both a and b

                Ans – a

 

26. The angle through which the motor turns for pulse is known as ---

                a. ramp angle

                b. rotational angle

                c. pulse angle

                d. step angle

                Ans – d

 

27. Wave excitation of a stepper motor results in ---

                a. microstepping

                b. half stepping

                c. incre. step angle

                d. reduced resolution

                Ans – b

 

28. Thevenin's volt is equal to  ---- volt. across the ---- terminals.

                a. short ckt, input

                b. short ckt, output

                c. open ckt, output

                d. open ckt, input

                Ans – c

 

29. Which parameter does not change during x'mer action in x'mer

                a. volt.

                b. current

                c. frequency

                d. voth a and b

                Ans – b

 

30.          With incre of load, the speed os induction motor operating in the stable region

                a. increases

                b. decr

                c. remains const

                d. incre. and then becomes constant

                Ans – b

 

31. The emf induced in the rotor of an induction motor is proportional to

                a. volt. applied to stator

                b. relative velocity between flux and rotor conductors

                c. both a and b

                d. slip

                Ans – c

 

32. The leakage flux in a x'mer depends upon

                a. the applied volt.

                b. load current

                c. the frequency

                d. the mutual flux

                Ans – b

 

33. What happens if field winding of the synchronous motor is short circuited

                a. 1st, starts as induction motor then run as synchronous motor

                b. not start

                c. motor will burn out

                d. run as induction mtor

                Ans – d

 

34. The x'mer ratings are usually expressed in terms of

                a. kva

                b. volt

                c. kw

                d. amperes

                Ans – a

 

35. Stray losses in dc generator are same as

                a. mechanical losses

                b. magnetic losses

                c. winding losses

                d. both a and b

                Ans – d

 

36. Which part will surely tell that given motor is dc motor not an ac motor

                a. windings

                b. shaft

                c. commutator

                d. stator

                Ans – c

 

37. For an induction motor, the rotor efficiency is -----

                a. P2/Pm

                b. P2/Pin

                c. Pm/P2

                d. Pout/Pin

                Ans – na

 

38. Unit of inductance is ---

                a. weber

                b. henry

                c. farad

                d. tesla

                Ans – b

 

39. In an induction motor, rotor runs at a speed of

                a. equal to speed of stator field

                b. lower than the speed of stator field

                c. higher than the speed of stator field

                d. having no relation with the speed of stator field

                Ans – a

 

40. In nodal analysis how many nodes are taken as reference nodes

                a. 1

                b. 2

                c. 3

                d. 4

                Ans – a

 

42. The power factor is unity for purely --- load

                a. inductive

                b. capacitive

                c. resistive

                d. both a and b

                Ans – c

 

43. A variable reluctance stepper motor is constucted of ----- material with salient poles.

                a. paramagnetic

                b. ferromagnetic

                c. diamagnetic

 

                d. non-magnetic

                Ans – b

 

 

44. In stepper motor, the position of shaft can be controlled bt controlling----

                a. supply volt.

                b. no. of input pulses

                c. no of poles

                d. flux

                Ans – b

 

45. A step up x'mer decreases

                a. volt

                b. current

                c. freq.

                d. power

                Ans – b

 

46. Efficiency if an ideal x'mer is

                a. 0.99

                b. 1

                c. 0.95

                d. 0.995

                Ans – b

 

47. Which one of the following accounts for smallest part os full load losses?

                a. magnetic losses

                b. mechanical losses

                c. field copper loss

                d. armature copper loss

                Ans – b

 

48. A super node is formed when

                a. there is a volt source with resistor bet 2 nodes

                b. there is a volt source without resistor bet 2 nodes

                c. there is a current source with resistor bet 2 nodes

                d. there is a current source without resistor bet 2 nodes

                Ans  -  a

 

49. ---- motor runs at synchronous speed only

                a. dc

                b. induction

                c. bldc

                d. stepper

                Ans - b

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