Question

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?

Answer 1

I = 300 A, l = 70 cm, r = 1.5 cm
F = \(\frac{\mu_{0} I_{1} I_{2}}{2 \pi r}\)
= \(\frac{4 \pi \times 10^{-5} \times 300 \times 300}{2 \times 1.5 \times 10^{-2}}\)
= 1.2 N
The force is repulsive.