A circular coil having N turns and radius r carries a current I. It is held in the XZ plane in a magnetic field `Bhati`. The torque on the coil due to the magnetic field is :

Options

A. `B pi r^(2) IN`
B. Zero
C. `(Br^(2)I)/(piN)`
D. `(B pi r^(2) I)/N`

Answer

A

Explanation

`bar(tau)=barm xxbarB , barB =Bhati , barm=[N(pir^(2))i]hatj`
`impliesvec(tau)=-[N pi r^(2)I . B]hatRimplies|bar(tau)|=pir^(2) NiB`