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

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Q. The back e.m.f. induced in a coil, when current changes from $1$ ampere to zero in one millisecond, is $4$ volts. The self-inductance of the coil is

Electromagnetic Induction

Solution:

$e=-L \frac{d i}{d t} ;$ But $e=4\, V$
and $\frac{d i}{d t}=\frac{0-1}{10^{-3}}=-1 / 10^{-3}$
$\therefore \frac{-1}{10^{-3}}(-L)=4=L=4 \times 10^{-3} H$