A circular coil carrying current I has a radius R and magnetic field at the centre is B . The distance from the centre along the axis of the same coil where the magnetic field will be B 8 is

Step-by-step solution

B center = μ 0 nI 2 R = B B x = B 8 = μ 0 nIR 2 2 ( R 2 + x 2 ) 3 / 2 1 8 μ 0 nI 2 R = μ 0 nIR 2 2 ( R 2 + x 2 ) 3 / 2 1 8 R 3 = 1 ( R 2 + x 2 ) 3 / 2 1 2 R = 1 ( R 2 + x 2 ) 1 2 4 R 2 = R 2 + x 2 x 2 = 3 R 2 x = 3 R