A current loop `ABCD` is held fixed on the plane of the paper as shown in figure. The arcs `BC( radius = b) and DA ( radius = a)` of the loop are joined by two straight wires `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 field (B) due to the loop `ABCD` at the origin (o) is :

Explanation

The magnitude of the magnetic field due to the loop ABCD at the origin (O) is :
(A) `(mu_(0)I(b-a))/(24ab)`
(B) `(mu_(0)I)/(4pi)[(b-a)/(ab)]`
(C ) `(mu_(0)I)/(4pi)[2(b-a)+(pi)/(3)(a+b)]`
(D) zero
Magnetic field due to loop ABCD
`=(mu_(0)I)/(4pi)((pi)/(6))xx[(1)/(a)-(1)/(b)]=(mu_(0)I)/(24)[(b-a)/(ab)]`
(ii) Due to the presence of the current `I_(1)` at the origin:
(A) The forces on AD and BC are zero.
(B) The magnitude of the net force on the loop is given by `(mu_(0)I_(1)I)/(4pi)[2(b-a)+(pi)/(3)(a+b)]`
(C ) the magnitude of the net force on the loop is given by `(mu_(0)II_(1))/(24ab)(b-a)`.
(D) the forces on AB and DC are zero.
`vecF=i(vec(l)xxvecB)` Magnetic field due to `I_(1)` is parallel to AD and BC. So that force On AD and BC is zero .