Question

Three straight parallel current-carrying conductors are shown in the figure. The force experienced by the middle conductor of length $25cm$ is

• A. $9\times 10^{-4}$ N toward left
• B. $3\times 10^{-4}$ N toward right
• C. $6\times 10^{-4}$ N toward right
• D. Zero

Answer 1

Answer: (B)

​ $\therefore$ Required force $=\frac{{\mu }_0}{2\pi }\left\{\frac{I{I}_2}{0.05}-\frac{I{I}_1}{0.03}\right\}L$
Assuming Left side is the $+\text{v}\text{e}$ direction
$=2\times 0.25\times 10^{-7}\left\{\frac{10\times 20}{0.05}-\frac{10\times 30}{0.03}\right\}N$ toward left
$=2\times 0.25\times 10^{-5}\left\{\frac{200}{5}-\frac{300}{3}\right\}$
$=2\times 0.25\times 10^{-5}\left\{40-100\right\}N$ toward left
$=2\times 0.25\times 60\times 10^{-5}N$ toward right
$=3\times 10^{-4}N$ toward right