In Fig., a semicircular wire is placed in a uniform field `vec B` directed towards right. Find the resultant magnetic force and torque on it.

Explanation

The wire is equivalent to

`becausetheta=0`
`thereforeF_("res")=0`
forces on individual parts are marked in the figure by `otimesandodot`. By symmetry their will be pair of forces forming couples.
`tau=int_(0)^(pi//2)i(Rd theta)Bsin(90-theta).2Rcostheta`

`tau=(ipiR^(2))/(2) " " rArr " " vectau=(ipiR^(2))/(2)B(-hatj)`