Question

A circular coil of `100` turns and having a radius of `0*05m` carries a current of `0*1A`. Calculate the work required to turn the coil in an external magnetic field of `1*5T` through `180^@` about an axis perpendicular to the magnetic field. The plane of the coil is initially at right angles to the magnetic field.

Answer 1

Correct Answer - `0*24J`
Here, `n=100`, `r=0*05m`, `I=0*1A`
`W=?`, `B=1*5T`,
`theta_1=0^@`, (When plane of coil is at `90^@` to B)
`theta_2=180^@`
`M=nIA=nI(pir^2)`
`=100xx0*1(3*14)(0*05)^2`
`=7*85xx10^-2Am^2`
`W=-MB(costheta_2-costheta_1)`
`=-7*85xx10^-2xx1*5(cos180^@-cos0^@)`
`W=0*24J`