Question

A long horizontally fixed wire carries a current of 100A. Directly above and parallel to it is another wire carrying a current of 20 A and weighing 0.04 N m^-1 . What should be the separation between the two wires so that the upper wire is just supported by magnetic repulsion?

• A. 1 cm
• B. 2 cm
• C. 3 cm
• D. 4 cm

Answer 1

The correct option is A

1 cm

$\frac{F}{I}=\frac{{\mu }_0{I}_1{I}_2}{2\pi r}\Rightarrow 0.04=\frac{(2\times {10}^{-7})\left(100\right)\left(20\right)}{r}\Rightarrow r=0.01m\Rightarrow r=1cm$