# Homework Help: Magnetism: Magnetic force between wires

1. Nov 1, 2004

### vsage

Magnetism: Magnetic field between wires

Two long parallel wires are a distance of d = 1 cm apart and carry equal antiparallel currents of 8 Amperes. Find the magnetic field intensity (in T) at the point P which is equidistant from the wires. (R = 10 cm).

This should be easy but I haven't gotten it right so far (as if that means it's hard). Here's what I did

$$B_1 = \frac{\mu_0i_i}{2\pi r_1}$$
$$B_1 = \frac{2\times 8}{\sqrt{0.1^2+0.005^2}}$$
= 1.598e-5 T roughly. Multiplied this by 2 since equal currents/radii in both wires. Vertical components cancel so I multiplied by $$\frac{0.1}{\sqrt{0.1^2+0.005^2}}$$ to get 3.192e-5 T. Where did I go wrong?

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Last edited by a moderator: Nov 1, 2004
2. Nov 1, 2004

### Staff: Mentor

It looks like you got the angles wrong. Don't forget that the magnetic field from each wire is perpendicular to the radial vector.

3. Nov 1, 2004

### vsage

Yeah thanks I figured that out a few minutes after I posted but forgot to mention that little detail. What was I thinking?! Used the dot product instead of the cross product. Whoops.