
Magnitude of magnetic fieldat point, $P$
$B = 2\left\{ {\frac{{{\mu _0}NI{R^2}}}{{2{{\left( {{R^2} + \frac{{{R^2}}}{4}} \right)}^{3/2}}}}} \right\}$
$=\frac{\mu_{0} N I R^{2}}{\frac{5^{3 / 2}}{8}}=\frac{8 \mu_{0} N I}{5^{3 / 2} R}$
What is the resistance of the given galvanometer? (In $\Omega$)
Reason : The magnetic field inside the solenoid is uniform.