(a) Draw a diagram showing the magnetic lines of force around the straight wire carrying current.

(a) The magnetic lines of force around a straight wire carrying current are concentric circles, lying in a plane perpendicular to the wire, with their centres on the wire, as shown below :

(b) On increasing the current through the wire, the strength of the magnetic field increases. The magnetic field lines become denser (i.e., more crowded) near the wire, and the field remains effective up to a larger distance from the wire.