Question

A long solenoid of radius $2$ cm has $100$ turns/cm and carries a current of $5A$. A coil of radius $1$ cm having $100$ turns and a total resistance of $20\Omega$ placed inside the solenoid co-axially. The coil is connected to galvanometer. If current in the solenoid is reversed in direction. Fine the charge flow 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

we Know that

$\begin{array}{c}q=\frac{2N\varphi }{R}\\ \varphi =n_1{\mu }_{0}i\pi r^{2}N\\ =100\times 4\pi \times {10}^{-7}\times 5\times {10}^{-4}\pi \times 100\\ \therefore q=\frac{2\times 100}{20}\times 100\times 4\pi \times {10}^{-7}\times 5\times {10}^{-4}\pi \times 100\\ =2\times {10}^{-4}C\\ Hence,theoptionAisthecorrectanswer.\end{array}$