Question

The flux associated with a coil changes from $1.35 \, Wb$ to $0.79 \, Wb$ 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, $I=\frac{E}{R}=\frac{d \phi}{R d t}$
$\Rightarrow Idt=\frac{d \phi}{R}$
Integrating,
$\displaystyle \int Idt=\displaystyle \int \frac{d \phi}{R}$
$\Rightarrow q=\frac{\phi}{R}$
If coil contains $N$ turns, then $q=\frac{N \phi}{R}$ .
If there is flux change $\Delta \phi$ , then $q=\frac{N \Delta \phi}{R}$ .
$\Rightarrow q=\frac{1}{7}\times \left(1.35 - 0.79\right)=0.08 \, C$