question_answer

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

[AIPMT (M) 2011]

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 :

[d]

\[{{\mathbf{F}}_{2}}=-{{\mathbf{F}}_{4}}\]

\[{{\mathbf{F}}_{1}}=\frac{{{\mu }_{0}}{{I}_{1}}Il}{2\pi d}\]

\[{{\mathbf{F}}_{2}}=\frac{{{\mu }_{0}}{{I}_{1}}Il}{2\pi (d+l)}\]

\[{{\mathbf{F}}_{1}}>{{\mathbf{F}}_{3}}\]

\[{{F}_{net}}={{F}_{1}}-{{F}_{3}}\]

So, wire attract loop.