Question

Three long straight parallel wires are kept as shown in the figure. The wire (3) carries a current I

(i) The direction of flow of current I in wire (3), is such that the net force, on wire (1), due to the other two wires, is zero.

(ii) By reversing the direction of I, the net force, on wire (2), due to the other two wires becomes zero. What will, be the direction current I, in the two cases ? Also obtain the relation between the magnitudes of currents I₁, I₂ and I.

Answer 1

(i) Force experienced by wire (1) can be zero only when the current in wire (3) flows along -j downward.

 (ii) When direction of current in wire (3) is reversed then current should be along + j i.e., upward.

For this case force on wire 2 becomes zero (given)