Question

A long straight vertical wire of diameter 2.0mm carries a steady current upwards. At 30mm from the centre of the wire, the magnetic field strength is 0.10mT. Sketch a graph to show the variation of magnetic field strength from the wire surface to a distance of 40mm from the centre of the wire. Calculate the magnetic field strength at

(a) the surface of the wire,

(b) 40mm from the centre of the wire.