Question

Two parallel very long straight wires carrying current of $5$A each are kept at a separation of $1$m. If the currents are in the same direction, the force per unit length between them is __________ N/m. $({\mu }_o=4\pi \times {10}^{-7}SI)$.

• A. $5\times {10}^{-5}$, attractive
• B. $5\times {10}^{-6}$, attractive
• C. $5\times {10}^{-5}$, repulsive
• D. $5\times {10}^{-6}$, repulsive

Answer 1

Answer: (B)

$5\times {10}^{-6}$, attractive

Given : $I_1=I_2=5A$ $d=1m$
Force per unit length between them $F=\frac{{\mu }_o{I}_1{I}_2}{2\pi d}$
$\therefore$ $F=\frac{4\pi \times {10}^{-7}\times 5\times 5}{2\pi \times 1}=5\times {10}^{-6}N/m$
Since current flows in the same direction in the wires, so the wires attract each other.
Correct answer is option B