Question

Three long, straight and parallel wires carrying currents are arranged as shown in figure. The force experienced by $10cm$ length of wire $Q$ is

• A. $1.4\times 10^{-4}N$ towards the right
• B. $1.4\times 10^{-4}N$ towards the left
• C. $2.6\times 10^{-4}N$ to the right
• D. $2.6\times 10^{-4}N$ to the left

Answer 1

Answer: (A)

Force on wire $Q$ due to wire $P$ is
$F_P=10^{-7}\times \frac{2\times 30\times 10}{0.1}\times 0.1$
$=6\times 10^{-5}N$
(Towards left)
Force on wire $Q$ due to wire $R$ is
$F_R=10^{-7}\times \frac{2\times 20\times 10}{0.02}\times 0.1$
$=20\times 10^{-5}N$
(Towards right)
Hence
$F_{net}=F_R-F_P$
$=14\times 10^{-5}N$
$=1.4\times 10^{-4}N$
(Towards right)