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# Two parallel wires carry currents $20A$ and $40A$ in the opposite directions. Another wire carrying a current $30A$ parallel to $40A$ is placed mid-way between the two wires. The force on it will be

$\begin {array} {1 1} (a)\;Towards\: 20A & \quad (b)\;Towards\: 40A \\ (c)\;Perpendicular \: to\: both\: 20A\: and\: 40A & \quad (d)\;Zero \end {array}$

Use the right hand rule to get the answer. The wires attract each other if the current in the wires are flowing in the same direction and repel each other if the currents are flowing in opposite direction. So the net force on the 30A wire  , pulls it toward the 40A wire.
Ans : (b)

edited Sep 18, 2014