Question

In a moving coil galvanometer, the coil having $500$ turns and an average area of $4 \,cm^{2}$ carries a current of $0.1 \,A$ and is set parallel to a magnetic field with a torque of $0.15\, N \,m$ . The strength of the magnetic field is

• A. $1\, T$
• B. $5T$
• C. $7.5 \, T$
• D. $50\, T$

Answer 1

Answer: (C)

$7.5 \, T$

Answer 2

Here,
$N=500, A=4\,cm^{2}$
$=4\times10^{-4}m^{2}$
$I=0.1\,A$,
$\tau=0.15\,N\,m$
As torque, $\tau=NIAB$
$\therefore B=\frac{\tau}{NIA}$
$=\frac{0.15\,Nm}{\left(500\right)\left(0.1A\right)\left(4\times10^{-4}m^{2}\right)}$
$=7.5\,T$