An electric current passes through a long straight wire. At a distance of 5 cm from the wire, the ma

Question

An electric current passes through a long straight wire. At a distance of 5 cm from the wire, the magnetic field is $B$. The magnetic field at 20 cm from the straight wire would be

Professor PC Thomas Classes · Answer

$B \propto 1/r$. If distance increases by $4$ times, magnetic field becomes $B/4$.