Question

A square current carrying loop is suspended in a uniform magnetic field acting in the plane of the loop. If the force on one arm of the loop is $F$, the net force on the remaining three arms of the loop is:

• A. $3F$
• B. $-F$
• C. $-3F$
• D. $F$

Answer 1

Answer: (B)

Forces, $F_1$ and $F_2$ acting on the coil are equal in magnitude and opposite in directions. As the forces $F_1$ and $F_2$ have the same line of action, their resultant effect on the coil is zero.

$\tau =NiBA\sin \theta$

${\tau }_{\max }=\mathrm{NiBA}\left(\theta =90^0\right)$

The two forces $F_3$ and $F_4$ are equal in magnitude and opposite in direction. As the two forces have different lines of action, they constitute a torque. Thus, if the force on one arm of the loop is $F$, the net force on the remaining three arms of the loop is $-F$.