22. The wires which connect the battery of an automobile to its starting motor carry a current of 300 A (for a short time). What is the force per unit length between the wires if they are 70 cm long and 1.5 cm apart? Is the force attractive or repulsive? 

Answers (1)
S Sayak

Since the distance between the wires is much smaller than the length of the wires we can calculate the force per unit length on the wires using the following relation.

F=\frac{\mu _{o}I_{1}I_{2}}{2\pi d}

Current in both wires=300 A

Distance between the wires=1.5 cm

Permeability of free space=4\pi \times10-7 TmA-1

F=\frac{4\pi \times 10^{-7}\times 300\times 300}{2\pi \times 0.015}

F=1.2 Nm-1

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