A long pair of insulated wires serves to conduct 24.5 A of dc current to and fro

Question

A long pair of insulated wires serves to conduct 24.5 A of dc current to and from an instrument. A third wire is placed in the plane of the two wires shown in (Figure 1) parallel and just to the right. If it carries 25.0 A upward, what force per meter of length does it exert on each of the other two wires? Assume it is 2.8mm from the nearest wire, center to center.  

Part A

Determine the force per meter exerted by the third wire on the right wire shown in the figure.

Express your answer using two significant figures.

Part B

Determine the direction of the force exerted by the third wire on the right wire shown in the figure.

Part C

Determine the force per meter exerted by the third wire on the left wire shown in the figure.

Express your answer using two significant figures.

Part D

Determine the direction of the force exerted by the third wire on the left wire shown in the figure.

Explanation / Answer

a) F/l = BI
B = 2kI'/r
F/l = 2kII'/r = 2*10^-7*24.5*25/2.8*10^-3 = 0.04375 N/m (repulsive)
b) Repulsive force, towards left
c) F/l = 2kII'/r = 2*10^-7*24.5*25/2.8*2*10^-3 = 0.021875 N/m (attractive)
d) Attractive force, towards right

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