Question

A varying current in a coil changes from $$10A$$  to zero in $$0.5\,\sec.$$  If the average e.m.f induced in the coil is $$220V,$$  the self-inductance of the coil is

A. $$5\,H$$
B. $$6\,H$$
C. $$11\,H$$  
D. $$12\,H$$
Answer :   $$11\,H$$
Solution :
Initial current $$\left( {{I_1}} \right) = 10\,A;$$   Final current $$\left( {{I_2}} \right) = 0;$$   Time $$\left( t \right) = 0.5\,\sec $$   and induced e.m.f. $$\left( \varepsilon \right) = 220\,V.$$   Induced e.m.f. $$\left( \varepsilon \right)$$
$$\eqalign{ & = - L\frac{{dI}}{{dt}} = - L\frac{{\left( {{I_2} - {I_1}} \right)}}{t} = - L\frac{{\left( {0 - 10} \right)}}{{0.5}} = 20L \cr & {\text{or,}}\,L = \frac{{220}}{{20}} = 11\,H\,\,\left[ {{\text{where }}L = {\text{Self inductance of coil}}} \right] \cr} $$

Releted MCQ Question on
Electrostatics and Magnetism >> Electromagnetic Induction

Releted Question 1

A thin circular ring of area $$A$$ is held perpendicular to a uniform magnetic field of induction $$B.$$ $$A$$ small cut is made in the ring and a galvanometer is connected across the ends such that the total resistance of the circuit is $$R.$$ When the ring is suddenly squeezed to zero area, the charge flowing through the galvanometer is

A. $$\frac{{BR}}{A}$$
B. $$\frac{{AB}}{R}$$
C. $$ABR$$
D. $$\frac{{{B^2}A}}{{{R^2}}}$$
Releted Question 2

A thin semi-circular conducting ring of radius $$R$$ is falling with its plane vertical in horizontal magnetic induction $$\overrightarrow B .$$  At the position $$MNQ$$  the speed of the ring is $$v,$$ and the potential difference developed across the ring is
Electromagnetic Induction mcq question image

A. zero
B. $$\frac{{Bv\pi {R^2}}}{2}$$  and $$M$$ is at higher potential
C. $$\pi RBv$$  and $$Q$$ is at higher potential
D. $$2RBv$$  and $$Q$$ is at higher potential
Releted Question 3

Two identical circular loops of metal wire are lying on a table without touching each other. Loop-$$A$$ carries a current which increases with time. In response, the loop-$$B$$

A. remains stationary
B. is attracted by the loop-$$A$$
C. is repelled by the loop-$$A$$
D. rotates about its $$CM,$$  with $$CM$$  fixed
Releted Question 4

A coil of inductance $$8.4 mH$$  and resistance $$6\,\Omega $$  is connected to a $$12 V$$  battery. The current in the coil is $$1.0 A$$  at approximately the time

A. $$500 s$$
B. $$25 s$$
C. $$35 ms$$
D. $$1 ms$$

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