Question

Two long parallel straight wires $A$ and $B$ carrying currents of $4.0 A$ and $5.0 \,A$ in same direction separated by a distance of $4 \times 10^{-2} m$. The force on a $0.20\, m$ section of wire $A$ is

• A. $2 \times 10^{-5} N$ towards $B$
• B. $2 \times 10^{-5} N$ away from $B$
• C. $2 \times 10^{-5} N$ perpendicular to $B$
• D. $2 \times 10^{-5} N$ parallel to $B$

Answer 1

Answer: (A)

$I_{1}=4 A , I_{2}=5 A , d=4 \times 10^{-2} \,m , l=0.20\, m$
Force on a current carrying wire,
$F =\frac{\mu_{0} I_{1} I_{2} l}{2 \pi d}$
$=\frac{4 \pi \times 10^{-7} \times 4 \times 5}{2 \times \pi \times 4 \times 10^{-2}} \times 0.20$
$=2 \times 10^{-5} N $ towards $ B$