(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

In the figure, the top wire is 1.1 mm-diameter copper wire and is suspended in air due to the two magnetic forces from the bottom two wires. The current is 45 A in each of the two bottom wires.

Calculate the required current flow in the suspended wire.

http://i37.tinypic.com/2u3v8sm.jpg

2. Relevant equations

F = mg

F(of wire1 on wire2) = I1 * I2 * u0 * length of wire2 / 2*pi*r

(second equation derived from equation from B, u0 * I / 2pi r)

3. The attempt at a solution

I've drawn a FBD with two forces going up (sin(60)* force from each of the two lower wires), and one force going down (that of gravity). I've set the two up equal to the one down.

(Force down = mg, and I calculated mg by using r^2 pi * length * density of copper (8.92 g/ cm^2) ). This allows the "length" factor to cancel out, since we're not told what it is.

Then I solved for the second current (since the first one is given as 45) ... unfortunately I'm not getting the right answer.

Any tips? Thank you!

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# Homework Help: Current in wire that's being held up magnetic field of two others

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