Question

A solenoid has $2000$ turns wound over a length of $0.30\, m$ . The area of its cross-section is $1.2 ? 10^{-3}\, m^2$. Around its central section, a coil of $300$ turn is wound. If an initial current of $2A$ in the solenoid is reversed in $0.25\, s$, then the emf induced in the coil is

• A. $6 ? 10^{-4}\, V$
• B. $4.8 ? 10^{-3}\, V$
• C. $6 ? 10^{-2}\, V$
• D. $48\,mV$

Answer 1

Answer: (D)

$48\,mV$

Answer 2

Induced emf $e=M \frac{di}{dt}$
$=\frac{\mu_{0}\,N_{1}\,N_{2}\,A}{l}. \frac{di}{dt}$
$=\frac{4\pi\times10^{-7}\times2000\times300\times1.2\times10^{-3}}{0.30}$
$\times\frac{\left|2-\left(-2\right)\right|}{0.25}$
$=48.2\times10^{-3}\,V=48\,mV$