Force between two perpendicular currents

[j-so16]

Homework Statement

Why is the force of a wire to another wire that is perpendicular to it zero?

Homework Equations

biot-savart law

The Attempt at a Solution

 

[Swap]

its because the magnetic field lines dut to one wire will be parallel to the another wire. And as the magnetic force is ilbsin(x) ad here the x is 0.

 

[merryjman]

the net force would be zero, but the net torque would not be. if you sketch this situation, and draw some field lines by one wire only (call it #2), you can use the RHR applied to wire #1, and because of #2's magnetic field, there would be a torque which would tend to make the two wires align parallel and carry current in the same direction.