question_answer

A square loop, carrying a steady current \[\text{I}\], is placed in a horizontal plane near a long straight conductor carrying a steady current \[{{\text{I}}_{\text{1}}}\]at a distance 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 perpendicular to the horizontal plane

C)  a net torque acting downward normal to the horizontal plane

D)  a net attractive force towards the conductor

Correct Answer: D

Solution :

\[{{\mathbf{F}}_{2}}=-{{\mathbf{F}}_{4}}\] \[{{\mathbf{F}}_{1}}=\frac{{{\mu }_{0}}{{I}_{1}}Il}{2\pi d}\] \[{{\mathbf{F}}_{2}}=\frac{{{\mu }_{0}}{{I}_{1}}Il}{2\pi (d+l)}\] \[{{\mathbf{F}}_{1}}>{{\mathbf{F}}_{3}}\] \[{{F}_{net}}={{F}_{1}}-{{F}_{3}}\] So, wire attract loop.