electromagnetic induction Mcqs
1. A small coil lies inside a large coil. The two coils are horizontal concentric and carry currents in opposite directions. The large coil will experience______________?
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A. No resultant force

B. A torque about horizontal axis

C. An upward force along the axis

D. A torque about vertical axis

2. Non inductive resistances are used in decreasing______________?
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A. Self inductance

B. Mutual inductance

C. Magnetic fields

D. Heating effect

3. An aeroplane of wingspan 10m flies from the equator towards the North Pole. The wings are perpendicular to the vertical component of the earths magnetic field (B = 410-5T). At maximum speed an emf of 96mV is induced across the wing tips. The maximum speed of the aeroplane is____________?
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A. 38.4msec-1

B. 200msec-1

C. 384msec-1

D. 150msec-1

4. The only difference between construction of D.C generator and A.C generator is that of_______________?
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A. commutator

B. coil

C. carbon brushes

D. magnetic field

5. A.C and D.C have the same______________?
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A. heating effect through a resistance

B. effect while passing through an inductance

C. effect in charging a capacitor

D. effect in charging a battery

6. A coil with negligible resistance has 50V across it with 10 mA. The inductive reactance is_____________?
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A. 500 ohms

B. 50 ohms

C. 5000 ohms

D. 1000 ohms

7. If current in a conductor increases then according to Lenzs law self-induced voltage will____________?
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A. tend to decrease the amount of cur-rent

B. aid the applied voltage

C. produce current opposite to the in-creasing current

D. aid the increasing current

8. The out put voltage of a transformer is 3 times the input voltage then turns ratio will be________________?
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A. 1

B. 3

C. 3-Jan

D. 6

9. Which of the following is unit of inductance ?
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A. Webers/metre

B. Ampere turns

C. Ohm

D. Henry
10. A metal rod of 25 cm length is moving at a speed of 0.5/sec in direction perpendicular to 0.25T magnetic field. Emf produced in the rod is_____________?
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A. 0.03125 volt

B. 0 volt

C. 31.25 volt

D. 3.125 volt

11. A coil of wire is arranged with its plane perpendicular to a uniform magnetic field o flux density B. when the radius of the coil increases from r1 to r2 in time ?t then what is the emf induced in the coil ?
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A. ?B(r2-r1)2/?t

B. ?B/r22-r12/?t

C. ?B(r22+r12)/?t

D. ?B(r22-r12)/?t
12. The property of coil by which a counter e.m.f. is induced in it when the current through the coil changes is known as__________?
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A. capacitance

B. series aiding inductance

C. mutual inductance

D. self-inductance
13. Which circuit element(s) will oppose the change in circuit current ?
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A. Capacitance only

B. Inductance only

C. Resistance only

D. Inductance and capacitance

14. A.C cannot be used for________________?
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A. producing light

B. producing heat

C. magnetizing and electroplating

D. all the above

15. The core of a coil has a length of 200 mm. The inductance of coil is 6 mH. If the core length is doubled, all other quantities, remaining the same, the inductance will be_____________?
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A. 48mH

B. 24mH

C. 12 mH

D. 3 mH
16. Current produced by moving the loop of wire across a magnetic field is called_____________?
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A. mean square current

B. A.C current

C. D.C current

D. induced current
17. Which of the fpllowing inductor will have the least eddy current losses ?
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A. Powdered iron core

B. Laminated iron core

C. Iron core

D. Air core
18. Two 300 uH coils in series without mutual coupling have a total inductance of___________?
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A. 150 uH

B. 300 uH

C. 600 uH

D. 75 uH

19. Which one of the following devices does not function like an electric motor ?
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A. Voltmeter

B. Ammeter

C. Transformer

D. Galvanometer

20. The self-inductance of a solenoid is increased when a soft iron core is inserted into it. This is because the soft iron core_______________?
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A. Reduces the effect of eddy current

B. Increases the mutual inductance between the solenoid and the core

C. Improves the flux linkage between the turns of the coil

D. Decreases the resistance of the solenoid

21. Magnetic compass needle will be deflecting if it is kept near________________?
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A. Accelerating charge

B. Soft iron

C. Static charge

D. Semi-conductor

22. Transformer works on the principle of________________?
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A. Law of conservation of power

B. Mutual induction

C. Lenzs law

D. Faradays law

23. When the motor is at its maximum speed then back emf will be______________?
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A. Zero

B. Maximum

C. No back emf

D. Intermediate values

24. Find the force acting on a conductor 3m long carrying a current of 50 amperes at right angles to a magnetic field having a flux density of 0.67 tesla
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A. 1000 N

B. 600 N

C. 400 N

D. 100 N
25. A crack in the magnetic path of an inductor will result in________________?
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A. reduced inductance

B. zero inductance

C. increased inductance

D. unchanged inductance

26. In case of an inductance, current is proportional to___________?
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A. voltage across the inductance

B. magnetic field

C. both A. and B.

D. neither (A) nor (B)

27. The magnitude of the induced e.m.f. in a conductor depends on the______________?
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A. flux density of the magnetic field

B. amount of flux linkages

C. rate of change of flux-linkages

D. amount of flux cut

28. A dynamo converts______________?
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A. magnetic energy into mechanical energy

B. electrical energy into mechanical energy

C. magnetic energy into electrical energy

D. mechanical energy into electrical energy
29. Which of the following circuit element stores energy in the electromagnetic field ?
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A. Variable resistor

B. Inductance

C. Resistance

D. Condenser

30. The self-inductance of the coil may be defined as equal to the e.m.f. induced in volts when the current in the circuit changes at the rate of unit Weber turns
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A. Yes

B. No
31. A laminated iron core has reduced eddy-current losses because____________?
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A. the laminations are stacked vertfcally

B. the magnetic flux is concentrated in the air gap of the core

C. the laminations are insulated from each other

D. more wire can be used with less D.C. resistance in coil

32. The direction of induced e.m.f. can be found by_____________?
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A. Flemings right hand rule

B. Laplaces law

C. Kirchhoff s voltage law

D. Lenzs law
33. Which of the following is not a unit of inductance ?
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A. Henry

B. Volt second per ampere

C. All of the above

D. Coulomb/volt ampere
34. Both the number of turns and the core length of an inductive coil are doubled. Its self-inductance will be_____________?
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A. unaffected

B. quadrupled

C. halved

D. doubled
35. The self inductances of two coils are 8 mH and 18 mH. If the co-efficients of coupling is 0.5, the mutual inductance of the coils is______________?
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A. 6 mH

B. 4 mH

C. 5 mH

D. 12 mH

36. The practical illustration of the phenomenon of mutual induction is____________?
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A. D.C dynamo

B. A.C generator

C. transformer

D. induction coil

37. An alternating current or voltage________________?
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A. varies in magnitude alone

B. changes its magnitude continuously and reverses its direction of flow after regularly recurring intervals.

C. fluctuates off and on

D. changes its direction again and again

38. The emf induced in a conductor of unit length moving with unit velocity at right angles to a magnetic field is equal to_____________?
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A. Motional emf

B. Magnetic flux density

C. Mutual induction

D. Torque

39. Power loss in actual transformer is due to_________________?
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A. Back emf

B. Eddy currents and magnetic hysterias

C. Small output

D. Soft iron core

40. Air-core coils are practically free from______________?
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A. hysteresis losses

B. eddy current losses

C. both (A) and (B)

D. none of the above

41. An open coil has_____________?
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A. zero resistance and high inductance

B. infinite resistance and zero inductance

C. infinite resistance and normal inductance

D. zero resistance and inductance

42. An e.m.f. of 16 volts is induced in a coil of inductance 4H. The rate of change of current must be______________?
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A. 32 A/s

B. 16 A/s

C. 64 A/s

D. 4 A/s
43. In case all the flux from the current in coil 1 links with coil 2, the co-efficient of coupling will be____________?
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A. zero

B. 1.0

C. 2

D. 0.5

44. The law that the induced e.m.f. and current always oppose the cause producing them is due to____________?
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A. Coulomb

B. Lenz

C. Newton

D. Faraday

45. emf induced in a circuit according to Faradays law depends on the_____________?
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A. maximum magnetic flux

B. initial magnetic flux

C. rate of change of magnetic flux

D. change in magnetic flux

46. Energy stored in a magnetic field is given by______________?
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A. LI2/2

B. LI2

C. IL2

D. L2I/2

47. A 200 turn coil has an inductance of 12 mH. If the number of turns is increased to 400 turns, all other quantities (area, length etc.) remaining the same, the inductance will be___________?
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A. 6 mH

B. 24 mH

C. 48 mH

D. 14 mH

48. Mutually inductance between two magnetically-coupled coils depends on____________?
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A. cross-sectional area of their common core

B. permeability of the core

C. the number of their turns

D. all of the above
49. Which one of the following functions like a motor ?
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A. galvanometer

B. all of above

C. ammeter

D. voltmeter

50. Two coils have self-inductances of 10 H and 2 H, the mutual inductance being zero. If the two coils are connected in series, the total inductance will be_____________?
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A. 8 H

B. 6 H

C. 12 H

D. 24 H