Question

Two straight wires each $10\,cm$ long are parallel to one another and separated by $2\,cm$ . When the current flowing in them is $30\,A$ and $40\,A$ respectively, the force experienced by either of the wires is

• A. $ 1.2\times 10^{-3} N $
• B. $ 12\times 10^{-3} N $
• C. $ 11.2\times 10^{-3} N$
• D. $ 10.2\times 10^{-3} N$

Answer 1

Answer: (A)

Force between two parallel wires is
$F=\frac{\mu_{0}}{4 \pi} \cdot \frac{2 I_{1} I_{2}}{r} \cdot l$
Given, $\mu_{0}=4 \pi \times 10^{-7}, I_{1}=30\, A, I_{2}=40\, A$
$l=10 \times 10^{-2} m, r-2 \times 10^{-2} m$
$F=\frac{4 \pi \times 10^{-7}}{4 \pi} \times \frac{2 \times 30 \times 40}{2 \times 10^{-2}} \times \frac{10}{100}$
$\Rightarrow F=1.2 \times 10^{-3} N$