A bar magnet has total length $2 l=20$ units and the field point $P$ is at a distance $d=10$ units f

Question

A bar magnet has total length $2 l=20$ units and the field point $P$ is at a distance $d=10$ units from the centre of the magnet. If the relative uncertainty of length measurement is $1 \%$, then uncertainty of the magnetic field at point $P$ is\

Professor PC Thomas Classes · Answer

(c) : As, $B=\frac{\mu_{0}}{4 \pi} \frac{m}{d^{3}}$ or $B \propto \frac{l}{d^{3}}$ $$ \frac{\Delta B}{B}=3 	imes\left(\frac{\Delta d}{d}ight)+\frac{\Delta l}{l} $$  %Uncertainty in $B=4 \%$\