A square loop, carrying a steady current $\mathrm{I}$, is placed in horizontal plane near a long straight conductor carrying a steady current $I_{1}$ at a distance of $\mathrm{d}$ from the conductor as shown in figure. The loop will experience

• A

  a net repulsive force away from the conductor
• B

  a net torque acting upward perpencicular to the hor izontal plane
• C

  a net torque acting downward normal to the hor izontal plane
• Correct answer
  D

  a net attractive force towards the conductor

Solution

$$ \begin{array}{l} \mathrm{F}_{2}=-\mathrm{F}_{4} \\ \mathrm{~F}_{1}=\frac{\mu_{0} \mathrm{I}_{1} \mathrm{I} l}{2 \pi \mathrm{d} l} \\ \mathrm{~F}_{2}=\frac{\mu_{0} \mathrm{I}_{1} \mathrm{I}}{2 \pi(\mathrm{d}+\mathrm{l})} \\ \mathrm{F}_{1}>\mathrm{F}_{3} \\ \mathrm{~F}_{\text {net }}=\mathrm{F}_{1}-\mathrm{F}_{3} \end{array} $$ So, wire attract loop.

Hence, the correct answer is option: 'D'.