Question

Two long conductors, separated by a distance d carry currents $I_1$ and $I_2$ in the same direction. They exert a force F on each other. Now the current in one of them is increased to two times and its direction is reversed. The distance is also increased to 3 times. The new value of the force between them is :

• A. $-\frac{2F}{3}$
• B. $\frac{F}{3}$
• C. $-2F$
• D. $-\frac{F}{3}$

Answer 1

The correct option is A $-\frac{2F}{3}$

Force due to two current carrying conductor is given by,
$F=\frac{{\mu }_0{I}_1{I}_2}{2\pi d}l$
$F^1=\frac{{\mu }_0{I}_1\times 2\times I_2}{2\pi \times 3d}l$ (direction is reversed)
$F^1=\frac{-2F}{3}$