An infinitely long, straight conductor `AB` is fixed and a current is passed through it. Another movable straight wire `CD` of finite length and carrying current is held perpendicular to it and released. Neglect weight of the wire

Options

A. The rod CD will move upwards parallel to itself
B. The rod CD will move downward parallel to itself
C. The rod CD will move upward and turn clockwise at the same time
D. The rod CD will move upward and turn anti –clockwise at the same time

Answer

C

Explanation

Direction of force -
`vecF = i_(2) (vecl xx vecB_(1))`
`vecB_(1) = (mu_(0) i_(1))/(2pi r) (-hatk)`
`vecl to hati`
`therefore (hatj) = hati xx (-hatk)` (upward)
There is non-uniform force increases and decreases as r increases. Torque will rotate rod CD clockwise.