A current loop ABCD is held fixed on the plane of the paper as shown in the figure. The arcs BC (radius = b) and DA radius = a) of the loop are joined by two straight wires AB and CD. A steady current I is flowing in the loop. Angle made by AB and CD at the origin O is `30^(@)`. Another straight thin wire with steady current `I_(1)` flowing out of the plane of the paper is kept at the origin.

The magnitude of the magnetic filed (B) due to loop ABCD at the origin (O) is :

Options

A. the forces on AB and DC are zero
B. the forces on AD and BC are zero
C. the magnitude of the net force on the loop is given by `(I_(1)I)/(4pi) mu_(0)[2(b-a)+(pi)/3(a+b)]`
D. the magnitude of the net force on the loop is given by `(mu_(0)II_(1))/(4ab)(b-a)`

Answer

B

Explanation

The straight wire is perpendicular to the segments and the fields are parallel. There will be no force. Due to parts AB and CD, their fields are equal and opposite and their effects also cancel each other.