Easy physics problem, need help finding forumula

1. Sep 13, 2004

rdn98

I have included a picture.

Question:
What is the force on each wire if B = 1.656T, i = 10A, L1 = 7cm and L2 = 14cm?

Now, I have checked my physics book, and the equation I have found is
F_12 = mu_0*L*I1*I2/(2*pi*D)

where D is the distance between the two wires, and L is the length of one wire.

However, I tried that formula in the computer, and it doesn't work. I let L =L2 (m), D=L1 (m), I have tried I1=10 and I2=+/- 10...but it didn't work.

I'm thinking there is another round about way to do this, but I don't know what. CAn someone lend me a hand?

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2. Sep 13, 2004

Juntao

Hey

Ok, the formula is right, you got all the information right under your nose. You're just interpreting wrong.

We know that the wires, lets denote them A and B, are going to have equal and opposite forces.

The equation is F_BA = I_B*L X(cross) B

F_BA = I_B*L * mu_0*I_A/(2*pi*D)
Ok, well, your B is already given to you, which you can substitute for the mu_0*I_A/(2*pi*D).

Let I_B = current, and your L = L2 and that should do the trick.

Well

3. Sep 13, 2004

Tide

Did you include the external magnetic field?