Two long parallel wires, AB and CD, carry equal currents in opposite directions. They lie in the x-y plane, parallel to the x-axis, and pass through the points (0,-a,0) and (0,a,0) respectively, Figure. The resultant magnetic field is:

Options

A. (i),(ii)
B. (ii),(iii)
C. (i),(ii)
D. (ii),(iv)

Answer

D

Explanation

On the axis
`B_(1)=(mu_(0)i)/(2pia)`, along `+z` axis
`B_(2)=(mu_(0)i)/(2pia)`, along `+z` axis
`B=B_(1)+B_(2)=(mu_(0)i)/(pia)`, along `+z`-axis
On the `z-` axis

Resultant of `B_(0), B_(0)` is `2B_(0) cos theta`, along `z-`axis