Question

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

• A. -2F
• B. F/3
• C. -2F/3
• D. -F/3

Answer 1

Answer: (C)

-2F/3

Answer 2

Force between two long conductor carrying current $F = \frac{\mu_{0}}{2\pi} \frac{I_{1}I_{2}}{d}\ell$ According to question $F' = \frac{\mu _{0}}{2\pi } \frac{\left(-2I_{1}\right)I_{2}}{d}\ell$ From equation $\left(i\right)$ and $\left(ii\right)$, $F' = -\frac{3}{2}F.$