Physics M.C.Q (1 Marks)

Energy stored in a coil of self inductance 40mH carrying a steady current of 2 A is

(a) 0.8 J

(b) 8 J

(c) 0.08 J

(d) 80 J

The self-induced e.m.f. in a 0.1 H coil when the current in it is changing at the rate of 200 ampere/second  is

(a) 8

(b) 8

(c) 20 V

(d) 125 V

The adjoining figure shows two bulbs B₁ and B₂ resistor R and an inductor L. When the switch S is turned off

(a) Both B1 and B2 die out promptly

(b) Both B1 and B2 die out with some delay

(c) B1 dies out promptly but B2 with some delay

(d) B2 dies out promptly but B1 with some delay

The current in a coil of inductance 5 H decreases at the rate of 2 A/s. The induced e.m.f. is

(a) 2 V

(b) 5 V

(c) 10 V

(d) – 10 V

Which of the following is not the unit of self inductance

(a) Weber/Ampere

(b) Ohm-Second

(c) Joule-Ampere

(d) Joule Ampere–2

Find out the e.m.f. produced when the current changes from 0 to 1 A in 10 second, given L = 10 mH

(a) 1 V

(b) 1 mV

(c) 1 mV

(d) 0.1 V

The current in a coil changes from 4 ampere to zero in 0.1 s. If the average e.m.f. induced is 100 volt, what is the self inductance of the coil

(a) 2.5 H

(b) 25 H

(c) 400 H

(d) 40 H

Eddy currents are used in

(a) Induction furnace	(b) Electromagnetic brakes
(c) Speedometers	(d) All of these

Two conducting circular loops of radii  and   are placed in the same plane with their centres coinciding. If , the mutual inductance M between them will be directly proportional to

(a)

(b)

(c)

(d)

What is the coefficient of mutual inductance when the magnetic flux changes by 2   and change in current is 0.01A

(a) 2 henry

(b) 3 henry

(c)  henry

(d) Zero

A coil of 100 turns carries a current of 5 mA and creates a magnetic flux of 10^–5 weber. the inductance is

(a) 0.2 mH

(b) 2.0 mH

(c) 0.02 mH

(d) None of these

A 100 mH coil carries a current of 1 ampere. Energy stored in its magnetic field is

(a) 0.5 J

(b) 1 J

(c) 0.05 J

(d) 0.1 J

A coil has an inductance of 2.5 H and a resistance of 0.5 r. If the coil is suddenly connected across a 6.0 volt battery, then the time required for the current to rise 0.63 of its final value is

(a) 3.5 sec

(b) 4.0 sec

(c) 4.5 sec

(d) 5.0 sec

An e.m.f. of 12 volt is produced in a coil when the current in it changes at the rate of 45 amp/minute. The inductance of the coil is

(a) 0.25 henry

(b) 1.5 henry

(c) 9.6 henry

(d) 16.0 henry

The equivalent inductance of two inductances is 2.4 henry when connected in parallel and 10 henry when connected in series. The difference between the two inductances is

(a) 2 henry

(b) 3 henry

(c) 4 henry

(d) 5 henry

The mutual inductance of an induction coil is 5H. In the primary coil, the current reduces from 5A to zero in  . What is the induced emf in the secondary coil

(a) 2500 V

(b) 25000V

(c) 2510V

(d) Zero

If in a coil rate of change of area is 5 m²/milli second and current become 1 amp from 2 amp in 2  If magnitude of field is 1 tesla then self inductance of the coil is

(a) 2 H

(b) 5 H

(c) 20 H

(d) 10 H

When the current through a solenoid increases at a constant rate, the induced current

(a) Is constant and is in the direction of the inducing current

(b) Is a constant and is opposite to the direction of the inducing current

(c) Increases with time and is in the direction of the inducing current

(d) Increases with time and opposite to the direction of the inducing current

A circular coil of radius 5 cm has 500 turns of a wire. The approximate value of the coefficient of self induction of the coil will be

(a) 25 millihenry	(b) 25  millihenry
(c) 50  millihenry	(d)  50 henry

The inductance of a solenoid 0.5 m long of cross-sectional area 20 cm² and with 500 turns is

(a) 12.5 mH

(b) 1.25 mH

(c) 15.0 mH

(d) 0.12 mH

The inductance of a coil is 60μH. A current in this coil increases from 1.0 A to 1.5 A in 0.1 second. The magnitude of the induced e.m.f. is

(a) 60

(b) 300

(c) 30

(d) 3

The number of turns of primary and secondary coils of a transformer are 5 and 10 respectively and the mutual inductance of the transformer is 25 henry. Now the number of turns in the primary and secondary of the transformer are made 10 and 5 respectively. The mutual inductance of the transformer in henry will be

(a) 6.25

(b) 12.5

(c) 25

(d) 50

An ideal coil of 10 henry is joined in series with a resistance of 5 ohm and a battery of 5 volt.  2 second after joining, the current flowing in ampere in the circuit will be

(a)

(b)

(c) (1 – e)

(d) e

If a current of 10 A flows in one second through a coil, and the induced e.m.f. is 10 V, then the self-inductance of the coil is

(a)

(b)

(c)

(d) 1 H

Which of the following is wrong statement

(a) An emf can be induced between the ends of a straight conductor by moving it through a uniform magnetic field

(b) The self induced emf produced by changing current in a coil always tends to decrease the current

(c) Inserting an iron core in a coil increases its coefficient of self induction

(d) According to Lenz's law, the direction of the induced current is such that it opposes the flux change that causes it

A varying current in a coil changes from 10 amp to zero in 0.5 sec. If average EMF is induced in the coil is 220 volts, the self inductance of coil is

(a) 5 H

(b) 10 H

(c) 11 H

(d) 12 H

If the current is halved in a coil, then the energy stored is how much times the previous value

(a)

(b)

(c) 2

(d) 4

The average e.m.f. induced in a coil in which a current changes from 0 to 2 A in 0.05 s is 8 V. The self inductance of the coil is

(a) 0.1 H

(b) 0.2 H

(c) 0.4 H

(d) 0.8 H

The energy stored in a 50 mH inductor carrying a current of 4 A will be

(a) 0.4 J

(b) 4.0 J

(c) 0.8 J

(d) 0.04 J

The mutual inductance between a primary and secondary circuits is 0.5 H. The resistances of the primary and the secondary circuits are 20 ohms and 5 ohms respectively. To generate a current of 0.4 A in the secondary, current in the primary must be changed at the rate of

(a) 4.0 A/s

(b) 16.0 A/s

(c) 1.6 A/s

(d) 8.0 A/s

The self inductance of a coil is L. Keeping the length and area same, the number of turns in the coil is increased to four times. The self inductance of the coil will now be

(a)

(b) L

(c) 4 L

(d) 16 L

A coil of self inductance 50 henry is joined to the terminals of a battery of e.m.f. 2 volts through a resistance of 10 ohm and a steady current is flowing through the circuit. If the battery is now disconnected, the time in which the current will decay to 1/e of its steady value is

(a) 500 seconds

(b) 50 seconds

(c) 5 seconds

(d) 0.5 seconds

A varying current at the rate of 3 A/s in a coil generates an e.m.f. of 8 mV in a nearby coil. The mutual inductance of the two coils is

(a) 2.66 mH

(b) 2.66

(c) 2.66 H

(d) 0.266 H

The current flowing in a coil of self inductance 0.4 mH is increased by 250 mA in 0.1 sec. The e.m.f. induced will be

(a) + 1 V

(b) – 1 V

(c) + 1 mV

(d) – 1 mV

In a coil of self inductance 0.5 henry, the current varies at a constant rate from zero to 10 amperes in 2 seconds. The e.m.f. generated in the coil is

(a) 10 volts

(b) 5 volts

(c) 2.5 volts

(d) 1.25 volts

An e.m.f. of 100 millivolts is induced in a coil when the current in another nearby coil becomes 10 ampere from zero in 0.1 second. The coefficient of mutual induction between the two coils will be

(a) 1 millihenry

(b) 10 millihenry

(c) 100 millihenry

(d) 1000 millihenry

When current in a coil changes to 2 ampere from 8 ampere in 3 , the e.m.f. induced in the coil is 2 volt. The self inductance of the coil in millihenry is

(a) 1

(b) 5

(c) 20

(d) 10

The momentum in mechanics is expressed as m × v. The analogous expression in electricity is

(a) I × Q

(b) I × V

(c) L × I

(d) L × Q

The unit of inductance is

(a) Volt/ampere

(b) Joule/ampere

(c) Volt-sec/ampere

(d) Volt-ampere/sec

The self inductance of a coil is 5 henry, a current of 1 amp change to 2 amp within 5 second through the coil. The value of induced e.m.f. will be

(a) 10 volt

(b) 0.10 volt

(c) 1.0 volt

(d) 100 volt

Mutual inductance of two coils can be increased by

(a) Decreasing the number of turns in the coils

(b) Increasing the number of turns in the coils

(c) Winding the coils on wooden core

(d) None of the above

Self induction of a solenoid is

(a) Directly proportional to current flowing through the coil

(b) Directly proportional to its length

(c) Directly proportional to area of cross-section

(d) Inversely proportional to area of cross-section

Two coils of self  inductance  and  are placed closer to each other so that total flux in one coil is completely linked with other. If M is mutual inductance between them, then

(a)

(b)

(c)

(d)

A coil is wound as a transformer of rectangular cross-section. If all the linear dimensions of the transformer are increased by a factor 2 and the number of turns per unit length of the coil remain the same, the self  inductance increased by a factor of

(a)  16

(b) 12

(c)  8

(d) 4

A coil and a bulb are connected in series with a dc source, a soft iron core is then inserted in the coil. Then

(a) Intensity of the bulb remains the same	(b) Intensity of the bulb decreases
(c) Intensity of the bulb increases	(d) The bulb ceases to glow

Two pure inductors each of self inductance L are connected in parallel but are well separated from each other. The total inductance is

(a) 2L

(b) L

(c)

(d)

5 cm long solenoid having 10 ohm resistance and 5 mH inductance is joined to a 10 volt battery. At steady state the current through the solenoid in ampere will be

(a) 5

(b) 1

(c) 2

(d) Zero

Two circuits have coefficient of mutual induction of 0.09 henry. Average e.m.f. induced in the secondary by a change of current from 0 to 20 ampere in 0.006 second in the primary will be

(a) 120 V

(b) 80 V

(c) 200 V

(d) 300 V

The inductance of a closed-packed coil of 400 turns is 8 mH. A current of 5 mA is passed through it. The magnetic flux through each turn of the coil is

(a)

(b)

(c)

(d)

An e.m.f. of 12 volts is induced in a given coil when the current in it changes at the rate of 48 amperes per minute. The self inductance of the coil is

(a) 0.25 henry

(b) 15 henry

(c) 1.5 henry

(d) 9.6 henry