The magnetic field at the centre of a circular coil of radius r , due to current I flowing through it, is B . The magnetic field at a point along the axis at a distance r 2 from the centre is :

Step-by-step solution

Magnetic field at the centre of the circle is, B = μ 0 i 2 R Magnetic field at the point on the axis is, B 2 = μ 0 i R 2 2 R 2 + x 2 3 2 ⇒ B 2 = μ 0 i R 2 2 R 2 + R 2 2 3 2 ⇒ B 2 = μ 0 i 2 5 4 3 2 R = 2 5 3 B