Question

In a moving coil galvanometer, the deflection ($\Phi$) on the scale by a pointer attached to the spring is

• A. $\left(\frac{NA}{kB}\right)I$
• B. $\left(\frac{N}{kAB}\right)I$
• C. $\left(\frac{NAB}{k}\right)I$
• D. $\left(\frac{NAB}{kI}\right)$

Answer 1

Answer: (C)

$\left(\frac{NAB}{k}\right)I$

Since magnetic torque on the coil, $\tau =NIAB$
This torque is balanced by counter torque
$\therefore k\varphi$ = $NIAB$ or $\varphi =\left(\frac{NAB}{k}\right)I$
where k is torsional constant. It is a scalar quantity having dimension of torque or energy i.e.$\left[M{L}^2{T}^{-2}\right].$