List of Electromagnetic Induction Objective Questions
1.The direction of incViced e.m.f. can be found by
Laplace’s law
Lenz’s law
Fleming’s right hand rule
Kirchhoff s voltage law
ANSWER : : Lenz’s law
2.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
3 mH
12 mH
24mH
48mH
ANSWER : : 3 mH
3.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
32 mH
38 mH
40 mH
48 mH
ANSWER : : 38 mH
4.As per Faraday’s laws of electromagnetic induction, an e.m.f. is induced in a conductor whenever it
lies perpendicular to the magnetic flux
lies in a magnetic field
cuts magnetic flux
moves parallel to the direction of the magnetic field
ANSWER : : cuts magnetic flux
5.Which of the following is not a unit of inductance ?
Henry
Coulomb/volt ampere
Volt second per ampere
All of the above
ANSWER : : Coulomb/volt ampere
6.Both the number of turns and the core length of an inductive coil are doubled. Its self-inductance will be
unaffected
doubled
halved
quadrupled
ANSWER : : doubled
7.If current in a conductor increases then according to Lenz’s law self-induced voltage will
aid the increasing current
tend to decrease the amount of cur-rent
produce current opposite to the in-creasing current
aid the applied voltage
ANSWER : : produce current opposite to the in-creasing current
8.The law that the induced e.m.f. and current always oppose the cause producing them is due to
Faraday
Lenz
Newton
Coulomb
ANSWER : : Lenz
9.Air-core coils are practically free from
hysteresis losses
eddy current losses
both (a) and (b)
none of the above
ANSWER : : both (a) and (b)
10.Which of the following circuit element stores energy in the electromagnetic field ?
Inductance
Condenser
Variable resistor
Resistance
ANSWER : : Inductance
11.An e.m.f. of 16 volts is induced in a coil of inductance 4H. The rate of change of current must be
64 A/s
32 A/s
16 A/s
4 A/s
ANSWER : : 4 A/s
12.Higher the self-inductance of a coil,
lesser its weber-turns
lower the e.m.f. induced
greater the flux produced by it
longer the delay in establishing steady current through it
ANSWER : : longer the delay in establishing steady current through it
13.An open coil has
zero resistance and inductance
infinite resistance and zero inductance
infinite resistance and normal inductance
zero resistance and high inductance
ANSWER : : infinite resistance and zero inductance
14.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
6 H
8 H
12 H
24 H
ANSWER : : 12 H
15.Which of the following circuit elements will oppose the change in circuit current ?
Capacitance
Inductance
Resistance
All of the above
ANSWER : : Inductance
16.The inductance of a coil will increase under all the following conditions except
when more length for the same number of turns is provided
when the number of turns of the coil increase
when more area for each turn is provided
when permeability of the core increases
ANSWER : : when more length for the same number of turns is provided
17.In case of an inductance, current is proportional to
voltage across the inductance
magnetic field
both (a) and (b)
neither (a) nor (b)
ANSWER : : magnetic field
18.A laminated iron core has reduced eddy-current losses because
more wire can be used with less D.C. resistance in coil
the laminations are insulated from each other
the magnetic flux is concentrated in the air gap of the core
the laminations are stacked vertf-cally
ANSWER : : the laminations are insulated from each other
19.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
increase
decrease
remain the same
initially increase and then decrease
ANSWER : : decrease
20.For a purely inductive circuit which of the following is true ?
Apparent power is zero
Relative power is.zero
Actual power of the circuit is zero
Any capacitance even if present in the circuit will not be charged
ANSWER : : Actual power of the circuit is zero
16.The inductance of a coil will increase under all the following conditions except
when more length for the same number of turns is provided
when the number of turns of the coil increase
when more area for each turn is provided
when permeability of the core increases
ANSWER : : when more length for the same number of turns is provided
17.In case of an inductance, current is proportional to
voltage across the inductance
magnetic field
both (a) and (b)
neither (a) nor (b)
ANSWER : : magnetic field
18.A laminated iron core has reduced eddy-current losses because
more wire can be used with less D.C. resistance in coil
the laminations are insulated from each other
the magnetic flux is concentrated in the air gap of the core
the laminations are stacked vertf-cally
ANSWER : : the laminations are insulated from each other
19.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
increase
decrease
remain the same
initially increase and then decrease
ANSWER : : decrease
20.For a purely inductive circuit which of the following is true ?
Apparent power is zero
Relative power is.zero
Actual power of the circuit is zero
Any capacitance even if present in the circuit will not be charged
ANSWER : : Actual power of the circuit is zero
21.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
4 mH
5 mH
6 mH
12 mH
ANSWER : s: c
22.The magnitude of the induced e.m.f. in a conductor depends on the
flux density of the magnetic field
amount of flux cut
amount of flux linkages
rate of change of flux-linkages
ANSWER : : rate of change of flux-linkages
23.Which of the following is unit of inductance ?
Ohm
Henry
Ampere turns
Webers/metre
ANSWER : : Henry
24.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
6 mH
14 mH
24 mH
48 mH
ANSWER : : 48 mH
25.Mutually inductance between two magnetically-coupled coils depends on
permeability of the core
the number of their turns
cross-sectional area of their com-mon core
all of the above
ANSWER : : all of the above
26.Which circuit element(s) will oppose the change in circuit current ?
Resistance only
Inductance only
Capacitance only
Inductance and capacitance
ANSWER : : Inductance only
27.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.
100 N
400 N
600 N
1000 N
ANSWER : : 100 N
28.Lenz’s law is a consequence of the law of conservation of
induced current
charge
energy
induced e.m.f.
ANSWER : : energy
29.A conductor 2 metres long moves at right angles to a magnetic field of flux density 1 tesla with a velocity of 12.5 m/s. The induced e.m.f. in the conductor will be
10 V
15 V
25V
50V
ANSWER : : 25V
30.The co-efficient of coupling between two air core coils depends on
self-inductance of two coils only
mutual inductance between two coils only
mutual inductance and self inductance of two coils
none of the above
ANSWER : : mutual inductance and self inductance of two coils
31.A coil is wound on iron core which carries current I. The self-induced voltage in the coil is not affected by
variation in coil current
variation in voltage to the coil
change of number of turns of coil
the resistance of magnetic path
ANSWER : : variation in voltage to the coil
32.Current changing from 8 A to 12 A in one second induced 20 volts in a coil. The value of inductance is
5 mH
10 mH
5 H
10 H
ANSWER : : 5 H
33.A coil induces 350 mV when the current changes at the rate of 1 A/s. The value of inductance is
3500 mH
350 mH
250 mH
150 mH
ANSWER : : 350 mH
34.A coil with negligible resistance has 50V across it with 10 mA. The inductive reactance is
50 ohms
500 ohms
1000 ohms
5000 ohms
ANSWER : : 5000 ohms
35.Two 300 uH coils in series without mutual coupling have a total inductance of
300 uH
600 uH
150 uH
75 uH
ANSWER : : 600 uH
36.An average voltage of 10 V is induced in a 250 turns solenoid as a result of a change in flux which occurs in 0.5 second. The total flux change is
20 Wb
2 Wb
0.2 Wb
0.02 Wb
ANSWER : : 0.02 Wb
37.A conductor carries 125 amperes of current under 60� to a magnetic field of 1.1 tesla. The force on the conductor will be nearly
50 N
120 N
240 N
480 N
ANSWER : : 120 N
38.A 500 turns solenoid develops an average induced voltage of 60 V. Over what time interval must a flux change of 0.06 Wb occur to produce such a voltage ?
0.01 s
0.1 s
0.5 s
5 s
ANSWER : : 0.5 s
39.A crack in the magnetic path of an inductor will result in
unchanged inductance
increased inductance
zero inductance
reduced inductance
ANSWER : : reduced inductance
40.Which of the fpllowing inductor will have the least eddy current losses ?
Air core
Laminated iron core
Iron core
Powdered iron core
ANSWER : : Air core