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 horizontal plane

Answer: (a). Near side of the loop carries I in the same direction as I₁: attraction towards the wire. Far side carries I opposite to I₁: repulsion, but it is farther away, so this force is smaller ( F ∝ 1/r). Forces on the two perpendicular sides are equal and opposite and cancel; all forces lie in the plane, so there is no torque. So the answer is (a) a net attractive force towards the conductor.

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Force on Current-Carrying Conductors

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

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Answer: (a)

Near side of the loop carries $I$ in the same direction as $I_1$ : attraction towards the wire.
Far side carries $I$ opposite to $I_1$ : repulsion, but it is farther away, so this force is smaller ( $F \propto 1/r$ ).
Forces on the two perpendicular sides are equal and opposite and cancel; all forces lie in the plane, so there is no torque.
So the answer is (a) a net attractive force towards the conductor.

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