Question

A circular coil of 100 turns and having an effective radius of `5cm` carries a current of `0*1` ampere. How much work is required to turn it in an external magnetic field of `1*5 weber//m^2` through `180^@` about an axis perpendicular to magnetic field. The plane of the coil is initially perpendicular to the magnetic field.

Answer 1

Here, `N=100, r=5cm=0*05m`,
`I=0*1amp., W=?, B=1*5Wb//m^2`,
`theta_1=0^@, theta_2=180^@`
Now, `area A =pir^2=3*14(0*05)^2sqm`
`W=-MB(costheta_2-costheta_1)`
`=-(NIA)B(costheta_2-costheta_1)`
`=-100xx0*1xx3*14(0*05)^2xx1*5[cos180^@-cos0^@]`
`=-31*4(0*05)^2xx1*5(-1,-1)=0*24J`