Electromagnetism question

Question

A vertical straight wire carrying an upward 12A current exerts an attractive force per unit length of 8.8E-4 N/m on a second parallel wire 7.0cm away. What current (magnitude and direction) flows in the second wire?

Answer 1

Force per unit length s given by F / L = µ₀I1I2 / 2πr. Solve for I2.

I2 = (F / L)(2πr / µ₀I1)

= ((8.8 x 10^-4 N) x ((2π x 0.07 m) / ((4π x 10^-7 Tm/A) x 12 A))

= 26 A downward