The charge which will flow through a galvanometer of resistance $200 \Omega$ connected to a $400 \Omega$…
The charge which will flow through a galvanometer of resistance $200 \Omega$ connected to a $400 \Omega$ circular coil of 1000 turns wound on a wooden stick $20 \mathrm{~mm}$ in diameter, if a magnetic field $\mathrm{B}=0.012 \mathrm{~T}$ parallel to the axis of the stick decreased suddenly to zero is nearly
$63 \mu \mathrm{C}$
$630 \mu \mathrm{C}$
$6.3 \mu \mathrm{C}$
$0.63 \mu \mathrm{C}$
Solution
Charge flowing through a circuit due to flux change is written as,
$\mathrm{q}=\frac{\Delta \phi}{\mathrm{R}}=\frac{\mathrm{NA}\left(\mathrm{B}_2-\mathrm{B}_1\right)}{\mathrm{R}}=\frac{\mathrm{N} \pi \mathrm{r}^2\left(\mathrm{~B}_2-\mathrm{B}_1\right)}{\mathrm{R}}$
On plugging the given values,
$q=\frac{1000 \times \pi \times 10^{-4} \times(0.012-0)}{(200+400)}$
On solving,
$q=6.3 \times 10^{-6}$