Question

Two parallel wires 1 m apart carry currents of 1 A and 3 A respectively in opposite directions. The force per unit length acting between two wires is

• A. $6\times {10}^{-5}N{m}^{-1}$ repulsive
• B. $6\times {10}^{-7}N{m}^{-1}$ repulsive
• C. $6\times {10}^{-5}N{m}^{-1}$ attractive
• D. $6\times {10}^{-7}N{m}^{-1}$ attractive

Answer 1

The correct option is B

$6\times {10}^{-7}N{m}^{-1}$ repulsive

$\frac{F}{L}=\frac{2{\mu }_0{I}_1{I}_2}{4\pi r}=\frac{2\times {10}^{-7}\times 1\times 3}{1}=6\times {10}^{-7}$ (repulsive)