Question

What is the direction of the magnetic field of a straight, current-carrying wire?

Answer 1

Direction of magnetic field.

The magnetic field lines due to straight conductor carrying current are in the form of concentric circles with the conductor as centre, lying in a plane perpendicular to the straight conductor. The direction of magnetic field lines is anticlockwise, if the current flows from A to B in the straight conductor Fig. 1(a) and is clockwise if the current flows from B to A in the straight conductor Fig. 1(b). The direction of magnetic field lines is given by Right Hand Thumb rule or maxwell's cork screw rule

Right hand thumb rule

According to this rule, if we imagine the linear wire conductor to be held in the grip of the right hand so that the thumb points in the direction of current, then the curvature of the fingers around the conductor will represent the direction of magnetic field lines, Fig. 2(a) and (b).

Maxwell's cork serew rule

According to this rule, if we imagine a right handed screw placed along the current carrying linear wire conductor, rotated such that the screw moves in the direction of flow of current, then the direction of rotation of the thumb gives the direction of magnetic lines of force. This rule is illustrated in Fig. 2(c)

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