ELECTROMAGNETIC INDUCTION

1. 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

1. self-inductance
2. mutual inductance
3. series aiding inductance
4. capacitance

Ans: a

2. As per Faraday's laws of electromagnetic induction, an e.m.f. is induced in a conductor whenever it

1. lies perpendicular to the magnetic flux
2. lies in a magnetic field
3.  cuts magnetic flux
4.  moves parallel to the direction of the magnetic field

Ans: c

3. Which of the following circuit element stores energy in the electromagnetic field ?

1. Inductance
2. Condenser
3. Variable resistor
4. Resistance

Ans: a

4. The inductance of a coil will increase under all the following conditions except

a.when more length for the same number of turns is provided

b.when the number of turns of the coil increase

3. when more area for each turn is provided
4. when permeability of the core increases

Ans: a

5. Higher the self-inductance of a coil,

1. lesser its weber-turns
2. lower the e.m.f. induced
3. greater the flux produced by it
4. longer the delay in establishing steady current through it

Ans: d

6. In an iron cored coil the iron core is removed so that the coil becomes an air cored coil.

The inductance of the coil will

1. increase
2. decrease
3. remain the same
4. initially increase and then decrease

Ans: b

7. An open coil has

1. zero resistance and inductance
2. infinite resistance and zero inductance
3. infinite resistance and normal inductance
4. zero resistance and high inductance

Ans: b

8. Both the number of turns and the core length of an inductive coil are doubled.

Its self-inductance will be

1. unaffected
2. doubled
3. halved
4. quadrupled

Ans: b

9. If current in a conductor increases then according to Lenz's law self-induced voltage will

1. aid the increasing current
2. tend to decrease the amount of cur-rent
3. produce current opposite to the in-creasing current
4. aid the applied voltage

Ans: c

10. The direction of incViced e.m.f. can be found by

1. Laplace's law
2. Lenz's law
3. Fleming's right hand rule
4. Kirchhoff s voltage law

Ans: b

11. Air-core coils are practically free from

1. hysteresis losses
2. eddy current losses
3. both (a) and (b)
4. none of the above

Ans: c

12. The magnitude of the induced e.m.f. in a conductor depends on the

1. flux density of the magnetic field
2. amount of flux cut
3. amount of flux linkages
4. rate of change of flux-linkages

Ans: d

13. Mutually inductance between two magnetically-coupled coils depends on

1. permeability of the core
2. the number of their turns
3. cross-sectional area of their com-mon core
4. all of the above

Ans: d

14. A laminated iron core has reduced eddy-current losses because

1. more wire can be used with less D.C. resistance in coil
2. the laminations are insulated from each other
3. the magnetic flux is concentrated in the air gap of the core
4. the laminations are stacked vertf-cally

Ans: b

15. The law that the induced e.m.f. and current always oppose the cause producing them is due to

1. Faraday
2. Lenz
3. Newton
4. Coulomb

Ans: b

16. Which of the following is not a unit of inductance ?

1. Henry
2. Coulomb/volt ampere
3. Volt second per ampere
4. All of the above

Ans: b

17. In case of an inductance, current is proportional to

1. voltage across the inductance
2. magnetic field
3. both (a) and (b)
4. neither (a) nor (b)

Ans: b

18. Which of the following circuit elements will oppose the change in circuit current ?

1. Capacitance
2. Inductance
3. Resistance
4. All of the above

Ans: b

19. For a purely inductive circuit which of the following is true ?

1. Apparent power is zero
2. Relative power is.zero
3. Actual power of the circuit is zero
4. Any capacitance even if present in the circuit will not be charged

Ans: c

20. Which of the following is unit of inductance ?

1. Ohm
2. Henry
3. Ampere turns

4. Webers/metre

Ans: b

21. An e.m.f. of 16 volts is induced in a coil of inductance 4H. The rate of change of current must be

1. 64 A/s
2. 32 A/s
3. 16 A/s
4. 4 A/s

Ans: d

22. 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 in ductance will be

1. 3 mH
2. 12 mH
3. 24mH (d)48mH

Ans: a

23. 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

1. 4 mH
2. 5 mH
3. 6 mH
4. 12 mH

Ans: c

24. Two coils have inductances of 8 mH and 18 mH and a co-efficient of coupling of 0.5. If the two coils are connected in series aiding, the total inductance will be

1. 32 mH
2. 38 mH
3. 40 mH
4. 48 mH

Ans: b

25. 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

1. 6 mH
2. 14 mH
3. 24 mH
4. 48 mH

Ans: d

26. 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

1. 6 H