Two parallel wires carry currents of `20 A` and `40 A` in same direction. Another wire carrying a current anti- parallel to `20 A` is placed midway between the two wires. The magnetic force on it will be

Options

A. towards `20 A`
B. towards `40 A`
C. zero
D. `_|_` to the plane of the currents

Answer

A

Explanation

Force on wire `③`:
Due to `①`, `F_(1) = k.(20 xx 20) = 400 k`, towards right
Due to `②`, `F_(2) = k.(20 xx 40) = 800k`, towards left
`F_(2) gt F_(1)`
Net force on middle wire is towards left.