State how the strength of the magnetic field produced at the centre of a coil by a current through the circular coil can be increased.

Explanation

The strenght of the magnetic field (B) produced at the centre of a coil by a current through a circular coil can be increased by -
(1) Increaseing the number of turns N of the coil `(B prop N)`.
(2) Increasing the current I through the coil `(B prop I)`.
(3) Decreasing the radius r of the coil `(B prop. (1)/(r))` .