(a) A circular coil of 30 turns and radius 8.0 cm carrying a current of 6.0 A is suspended vertically in a uniform horizontal magnetic field of magnitude 1.0 T. The field lines make an angle of `60^@` with the normal of the coil. Calculate the magnitude of the counter torque that must be applied to prevent the coil from turning. (b) Would your answer change, if the circular coil in (a) were replaced by a planar coil of some irregular shape that encloses the same area? (All other particulars are also unaltered.)

Explanation

(a) According to formula, we have,
`tau=BINAsintheta`
= `BIN(piR^(2))sintheta`
= `(1)(6)(30)(3.14)(0.08)^(2)sin60^(@)`
= `(180)(3.14)(64xx10^(-4))(0.866)`
`thereforetau=3.132Nm`
(b) Here, formula `tau=BINAsintheta` is true for any shape of planar coil. Hence, for same area of another planar coil, our answer will not change by changing only shape of planar coil.