Three long, parallel, straight wires pass through the vertices of an equilateral

Question

Three long, parallel, straight wires pass through the vertices of an equilateral triangle that has sides L = 13.8 cm, as shown in the figure below. A a dot indicates that the direction of the current is out of the screen and a cross indicates that the direction of the current is into the screen. Each current is 18.0 A.

(a) Find the magnetic field at the location of the upper wire due to the currents in the two lower wires.

magnitude:............................. µT

direction?

(b) Find the force per unit length on the upper wire.

magnitude................... N/m

direction?

Explanation / Answer

a) B = 2 * (mu0 i / 2 pi r) * cos theta

= [2 * 2 * 10-7 * 18 / 0.138] * 0.866

magnetic field = 4.52 * 10-5 T = 45.2 muT

direction will be towards the right

b) F/L = i B = 18 * 4.52 * 10-5

force per unit length on the upper wire = 8.13 * 10-4 N/m

direction will be straight up the page

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