Question

The flux associated with a coil changes from $1.35Wb$ to $0.79Wb$ within $\frac{1}{10}s$ . Then the charge which flows in the coil, if resistance of coil is $7\Omega$ is

• A. $0.08C$
• B. $0.8C$
• C. $0.008C$
• D. $8C$

Answer 1

Answer: (A)

As, $I=\frac{E}{R}=\frac{d\varphi }{Rdt}$
$\Rightarrow Idt=\frac{d\varphi }{R}$
Integrating,
$\int Idt=\int \frac{d\varphi }{R}$
$\Rightarrow q=\frac{\varphi }{R}$
If coil contains $N$ turns, then $q=\frac{N\varphi }{R}$ .
If there is flux change $\Delta \varphi$ , then $q=\frac{N\Delta \varphi }{R}$ .
$\Rightarrow q=\frac{1}{7}\times \left(1.35-0.79\right)=0.08C$