Question

If the coefficient of mutual induction of the primary and secondary coils of an induction coil is $5\, H$ and a current of $10 A$ is cut-off in $5 \times 10^{-4} s$, the emf inducted (in volt) in the secondary coil is :

• A. $5 \times 10^{4}$
• B. $1 \times 10^{5}$
• C. $25 \times 10^{5}$
• D. $5 \times 10^{6}$

Answer 1

Answer: (B)

$1 \times 10^{5}$

Answer 2

The induced emf $e$ in the secondary is given by
$e=-\frac{d \phi}{d t}=-M \frac{d I}{d t}$
Or $|e|=M \frac{d I}{d t}$
$\therefore |e| =5 \times \frac{10}{5 \times 10^{-4}}$
$=1 \times 10^{5} \,V$