Two long straight parallel wieres are `2m` apart, perpendicular to the plane of the paper. The wire A carries a current of `9.6 A`, directed into the plane of the paper. The wire `B` carries a current such that the magnetic field of induction at the point `P`, at a distance of `10/11` m from the wire B, is zero. find
a. the magnitude and directiion of the current in B.
b. the magnitude of the magnetic field of induction of the pont `S`.
c. the force per unit length on the wire `B`.

Options

A. `1A`
B. `2A`
C. `3A`
D. `4A`

Answer

C

Explanation

Since magnetic field at `P` is zero, direction of current in `B` should be opposite to current in `A` i.e. outside the plane of paper.
`B_(P)=0`
`B_(A)=B_(B)`
`(mu_(0)(9.6))/(2pi(2+10/11))=(mu_(0)i)/(2pi(10/11)) implies 9.6/((32/11))=i/((10/11))`
`i=3 A`