Question

An infinite current carrying wire passes through point O and in perpendicular to the plane containing a current carrying loop ABCD as shown in the figure. Choose the correct option (s) :

• A. net force on the loop is zero
• B. net torque on the loop is zero
• C. as seen from O, the loop rotates clockwise
• D. as seen from O, the loop rotates anticlockwise

Answer 1

Answer: (A), (C)

The correct options are
A net force on the loop is zero
C as seen from O, the loop rotates clockwise

Force on part AB=$BIL=\frac{{\mu }_0{I}_1}{2\pi r_1}I{L}_{AB}$

$=\frac{{\mu }_0{I}_1}{2\pi r_1}I(\frac{\varphi }{2\pi }2\pi r_1)=\frac{{\mu }_{0}I{I}_1\varphi }{2\pi }$

This force is inwards.

Force on part CD=$BIL=\frac{{\mu }_0{I}_1}{2\pi r_2}I{L}_{CD}$

$=\frac{{\mu }_0{I}_1}{2\pi r_2}I(\frac{\varphi }{2\pi }2\pi r_2)=\frac{{\mu }_{0}I{I}_1\varphi }{2\pi }$

This force is outwards.

Hence net force is zero.

Force on BC acts upwards, force on AD acts downwards.

Thus it appears rotating clockwise as seen from O.