Question

What is the self-inductance of a coil which produces $$5\,V$$  when the current changes from $$3\,A$$  to $$2\,A$$  in one millisecond ?

A. $$5000\,H$$
B. $$5\,mH$$  
C. $$50\,H$$
D. $$5\,H$$
Answer :   $$5\,mH$$
Solution :
Emf induced in the coil is given by $$e = - \frac{{d\phi }}{{dt}}$$
If coil has self-inductance $$\left( L \right)$$ and current $$i,$$ then induced emf is given by
$$\eqalign{ & e = - \frac{d}{{dt}}\left( {Li} \right)\,\,{\text{or}}\,\,e = - L\frac{{di}}{{dt}} \cr & \therefore L = \frac{{\left| e \right|}}{{\frac{{di}}{{dt}}}} \cr} $$
$$\eqalign{ & {\text{Given,}}\,\,\left| e \right| = 5\,V,di = 3 - 2 = 1\,A \cr & dt = 1\,ms = 1 \times {10^{ - 3}}s \cr & \therefore L = \frac{{5 \times {{10}^{ - 3}}}}{1} = 5\,mH \cr} $$

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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Electromagnetic Induction


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