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  4. The back emf 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

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Q. The back emf 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

BITSATBITSAT 2010

Solution:

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