You are given two infinite, parallel wires each carrying current I. The wires are separated by a distance d, and the current in the two wires is flowing in the same direction. This problem concerns the force per unit length between the wires.

What is the force per unit length F/L between the two wires?

Explanation:

Since current is flowing in the same direction in both the wires , they will attract each other .

Magnetic field due to first wire on second wire

B = (μ₀ / 4π) x 2I / d  , I is current on first wire and d is distance of second wire

Force on length L on second wire

F = B I L , B is magnetic field , I is current in second wire and L is length of second wire .

force per unit length of second wire

F/L = B I

= (μ₀ / 4π) x 2I / d X I

= 10⁻⁷ x 2 x I² / d

The same force will apply on first wire due to second wire as action and reaction forces are equal and opposite.

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