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

Question

Three long, parallel, straight wires pass through the corners of an equilateral triangle of sides 10 cm as shown in the figure below, where a dot means that the current is out of the paper and a cross means that it is into the paper.

Suppose each current is 11.9 A and that the direction of the current in the lower-right wire is now reversed.

(a) Find the magnetic field B at the upper wire due to the two lower wires.
B = __________ T

(b) Find the force per unit length on the upper wire.
F/l = __________ N/m

Three long, parallel, straight wires pass through the corners of an equilateral triangle of sides 10 cm as shown in the figure below, where a dot means that the current is out of the paper and a cross means that it is into the paper. Suppose each current is 11.9 A and that the direction of the current in the lower-right wire is now reversed. (a) Find the magnetic field B at the upper wire due to the two lower wires. B = __________ T (b) Find the force per unit length on the upper wire. F/l = __________ N/m

Explanation / Answer

a) B = 2 [mu / 4 pi] [2 I / R] cos 30

= 2 [10-7] [2 *11.9 / 0.10] cos 30

= 41.2 muT

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b)force per unit length on the upper wire

= 4 [mu / 4 pi] [ I2 / R] cos 30

= 4 [10-7] [11.92 / 0.10] cos 30

= 4.91 * 104 N/m

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