Question

A long solenoid of radius $2cm$ has $100$ turns/cm and carries a current of $5A$. A coil of radius $1cm$ having $100$ turns and a total resistance of $20\Omega$ is placed inside the solenoid coaxially. The coil is connected to a galvanometer. If the current in the solenoid is reversed in direction, find the charge flown through the galvanometer.

• A. $2\times {10}^{-4}C$
• B. $1\times {10}^{-4}C$
• C. $4\times {10}^{-4}C$
• D. $8\times {10}^{-4}C$

Answer 1

The correct option is A $2\times {10}^{-4}C$

$Q=\frac{NBA}{l}$ where $B={\mu }_{0}ni$ and $n={10}^4{m}^{-1}$

$⟹Q=\frac{4\pi \times {10}^{-7}\times 100\times 5\pi \times {10}^{-4}}{20}$

$=2\times {10}^{-4}C$