Another Right Hand Thumb Rule, stated differently, can be used to find the direction of magnetic field at the centre of a circular coil carrying current. It is as follows:
When the current (I) is flowing through a circular coil and if we imagine the fingers of the right hand curling in the direction of the current, the thumb will point in the direction of the magnetic field (B) at its centre. Applying this rule, we find that for a circular current-carrying coil with its plane perpendicular to the plane of the paper:
(i) B is along the axis of the coil and is acting upward,
(ii) B is along the axis of the coil and is acting downward,
