Question

State and explain Maxwell's right-hand thumb rule.

Answer 1

Maxwell’s right-hand thumb rule indicates the direction of magnetic field if the direction of current is known.
According to this rule, if we grasp the current-carrying wire in our right hand so that our thumb points in the direction of current, the direction in which our fingers encircle the wire will give the direction of magnetic field lines around the wire.
When thumb points upwards, the curled fingers are anticlockwise. So, the direction of magnetic field is anticlockwise. 
When thumb points downwards, the curled fingers are clockwise. So, the direction of magnetic field is clockwise.