Question: Two parallel wires carrying currents I₁ and I₂ in the same direction are separated by a distance d. What is the force per unit length between them?

Options:

1. (μ₀I₁I₂)/(2πd)
2. (μ₀I₁I₂)/(4πd)
3. (μ₀I₁I₂)/(8πd)
4. (μ₀I₁I₂)/(πd)

Correct Answer: (μ₀I₁I₂)/(2πd)

Solution:

The force per unit length between two parallel wires is given by F/L = (μ₀I₁I₂)/(2πd).