\(\mathrm{A}, \mathrm{B}\) and \(\mathrm{C}\) are three parallel conductors of equal lengths carrying currents I, I and 2I respectively. Distance between A and \(B\) is ' \(x\) ' and that between B and \(C\) is also ' \(x\) '. \(F_1\) is the force exerted by conductor \(\mathrm{B}\) on \(\mathrm{A}\). \(\mathrm{F}_2\) is the force exerted by conductor \(\mathrm{C}\) on \(\mathrm{A}\). Current \(\mathrm{I}\) in \(\mathrm{A}\) and \(\mathrm{I}\) in \(\mathrm{B}\) are in same direction and current \(2 \mathrm{I}\) in \(\mathrm{C}\) is in opposite direction. Then

Current in A and B are in the same direction. Hence force \(F_1\) exerted by B on A will be attractive (towards B). Current in A and \(\mathrm{C}\) are in opposite directions. Hence force \(\mathrm{F}_2\), exerted by \(\mathrm{C}\) on A will be repulsive (away from \(C\) ). Thus \(F_1\) and \(F_2\) are opposite in direction.

\(
\begin{aligned}
& \mathrm{F}_1=\frac{\mu_0}{2 \pi} \cdot \frac{\mathrm{I}_1 \mathrm{I}_2}{\mathrm{x}} \cdot \mathrm{L}=\frac{\mu_0}{2 \pi} \cdot \frac{\mathrm{I}^2}{\mathrm{x}} \mathrm{L} \\
& \mathrm{F}_2=\frac{\mu_0}{2 \pi} \cdot \frac{2 \mathrm{I}^2}{2 \mathrm{x}} \cdot \mathrm{L}=\frac{\mu_0}{2 \pi} \cdot \frac{\mathrm{I}^2}{\mathrm{x}} \cdot \mathrm{L}
\end{aligned}
\)
\(\therefore \mathrm{F}_1\) and \(\mathrm{F}_2\) have some magnitude.
\(
\therefore \mathrm{F}_1=-\mathrm{F}_2
\)