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Question: The back e.m.f. induced in a coil, when current changes from 1 ampere to zero in one milli‑second, i...

The back e.m.f. induced in a coil, when current changes from 1 ampere to zero in one milli‑second, is 4 volts, the self inductance of the coil is

A

1 H

B

4 H

C

10−310^{- 3} H

D

4×10−34 \times 10^{- 3} H

Answer

4×10−34 \times 10^{- 3} H

Explanation

Solution

e=−Ldidte = - L\frac{di}{dt} but e =4V and didt=0−110−3=−1/10−3\frac{di}{dt} = \frac{0 - 1}{10^{- 3}} = - 1/10^{- 3}

∴ 6mu−110−3(−L)=4⇒L=4×10−3henry\therefore\mspace{6mu}\frac{- 1}{10^{- 3}}( - L) = 4 \Rightarrow L = 4 \times 10^{- 3}henry