Question

A square loop, carrying a steady current $I$, is placed in a horizontal plane near a long straight conductor carrying a steady current $I_1$, at a distance d from the conductor as shown in figure. The loop will experience

• A. a net attractive force towards the conductor
• B. a net repulsive force away from the conductor
• C. a net torque acting upward perpendicular to the horizontal plane
• D. a net torque acting downward normal to the horizontal plane

Answer 1

Answer: (A)

$\overrightarrow{F_2}=-{\vec{F}}_4$
$\overrightarrow{F_1}=\frac{{\mu }_0{I}_1{I}_2\ell }{2\pi d}$
$\overrightarrow{F_3}=\frac{{\mu }_0{I}_1{I}_2\ell }{2\pi (d+\ell )}$
${\vec{F}}_1>F_3$
So wire attract loop.