Question

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

• A. $9 \times 1 0^{- 4}$ N toward left
• B. $3 \times 1 0^{- 4}$ N toward right
• C. $6 \times 1 0^{- 4}$ 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
$=2\times 0.25\times 10^{- 7}\left\{\frac{1 0 \times 2 0}{0 . 05} - \frac{1 0 \times 3 0}{0 . 03}\right\}N$ toward left
$= 2 \times 0.25 \times 1 0^{- 5} \left\{\frac{2 0 0}{5} - \frac{3 0 0}{3}\right\}$
$=2\times 0.25\times 10^{- 5}\left\{4 0 - 1 00\right\}N$ toward left
$=2\times 0.25\times 60\times 10^{- 5}N$ toward right
$=3\times 10^{- 4}N$ toward right