Question

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

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

Answer 1

Answer: (B)

$2.4\times {10}^{-2}V$

$n=\frac{N}{l}=\frac{2000}{0.3}=\frac{20000}{3}$

$\xi =\frac{d}{dt}\left(NBA\right)=NA\frac{dB}{dt}$

Since $B={\mu }_{0}nI$

$\Rightarrow \xi =\left(\mu NAn\right)\frac{dI}{dt}\Rightarrow \xi =0.024V$