Question

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 .

Due to the process of the current `I_(1)` at the origin:
A. The forcwes on `AD and BC` are zero.
B. The magnitude of the net force on the loop is given by
`(I_(1)I)/( 4 pi) mu_(0)[2 ( b-a)+pi//3( a+b)]`
C. The magnitude of the net force on the loop is given by `(mu_(0)II)/( 24 ab) ( b-a)`
D. The forces on `AB and DC` are Zero.

Answer 1

Correct Answer - A
KEY CONCEPT : `vec(F) = I(vec(l)xxvec(B)) `
The force on `AD and BC` due to corrent `I_(1)` is zero. This is because the directions of current element `Ivec(dl)` and magnetic field `vec(B)` are parallel.