Question

A solenoid has $2000$ turns wound over a length of $0.3m$. The area of its cross section is $1.2\times {10}^{-3}{m}^2$. Around its cross section a coil of $300$ turns is wound. If an initial current of $2A$ is reversed in $0.25s$, the emf induced in the coil is equal to

• A. $6\times {10}^{-4}V$
• B. $4.8\times {10}^{-2}V$
• C. $2.4\times {10}^{-2}V$
• D. $48kV$

Answer 1

Answer: (B)

$4.8\times {10}^{-2}V$

Induces emf, $e=M\frac{di}{dt}=\frac{{\mu }_0{N}_1{N}_{2}A}{l}\frac{di}{dt}$

$=\frac{4\pi \times {10}^{-7}\times 2000\times 300\times 1.2\times {10}^{-3}}{0.30}\frac{2-(-2)}{0.25}$

$=4.8\times {10}^{-2}V$