An equilateral triangle frame `PQR` of mass `M` and side a is kept under the influence of magnetic force due to inward perpendicular magnetic field `B` and gravitational field as shown in the figure. The magnitude and direction of current in the frame so that the frame remains at rest is

Options

A. `I=(2Mg)/aB`, anti clockwise
B. `I=(2Mg)/(aB)`, clockwise
C. `I=(Mg)/(aB)`, anticlockwise
D. `I=(Mg)/(aB)`, clockwise

Answer

B

Explanation

`F_(MNPQ)= F_(MQ)` and this force should be upwards to balance the weight.

`:. ilB=mg`, where
`l=MQ=a/2`
`:. i(a/2)B=mg or i=(2Mg)/(aB)`
force is upwards if current is clockwise or current in `MQ` is towards right.