Two wires of same length are shaped into a square and a circle. If they carry same current, ratio of the magnetic moment is

Options

A. `2 : pi `
B. `pi : 2`
C. `pi : 4`
D. `4 : pi`

Answer

C

Explanation

For square , 4A = `I implies A = l//4`
`m_(1) = NIA = 1 xx I xx ((l)/(4))^(2)`
For circle , `2pi = I implies r = (l)/(2pi)`
`m_(2) = I xx pi ((l)/(2pi))^(2)`
`implies (m_(1))/(m_(2)) = (l^(2))/(16) xx (4pi)/(l^(2)) = pi :4`