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

Suppose length of each wire is l
`A_("square") = ((l)/(4))^(2) = (l^(2))/(16)`
`therefore` Magnetic moment

M = 1A
`(M_("square"))/(M_("circle")) = (A_("square"))/(A_("circle"))`

`(l^(2))/(16) xx (4pi)/(l^(2)) = (pi)/(4)`
`(M_(s))/(M_(c)) = (pi)/(4)`