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

Maxwell’s right-hand thumb rule indicates the direction of the magnetic field if the direction of current is known.

According to this rule, if we hold the current-carrying wire in our right hand so that our thumb points in the direction of the current, the direction in which our fingers wrap the wire will give the direction of magnetic field lines around the wire.

When thumb points upwards, the wrapped fingers are anticlockwise. So, the direction of the magnetic field is anticlockwise.

When thumb points downwards, the wrapped fingers are clockwise. So, the direction of the magnetic field is clockwise.