Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): A rectangular current loop placed in a uniform magnetic field experiences a net force.
Reason (R): In a uniform magnetic field, the forces on opposite arms of a rectangular current loop are equal in magnitude and opposite in direction.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A) is not correct but (R) is correct.
Assertion (A) A rectangular current loop placed in a uniform magnetic field experiences a net force. — False. The forces on the four arms add up to zero. So the loop has no net force and does not move as a whole. It feels only a torque, which tends to turn it.
Reason (R) In a uniform magnetic field, the forces on opposite arms of a rectangular current loop are equal in magnitude and opposite in direction. — True. Opposite arms carry the current in opposite directions. They have the same length and lie in the same field, so the forces on them are equal and opposite.
NCERT (2026-27):
Torque on a rectangular current loop in a uniform magnetic field – “We now show that a rectangular loop carrying a steady current I and placed in a uniform magnetic field experiences a torque. It does not experience a net force.”
Torque on a rectangular current loop in a uniform magnetic field – “The forces on the arms BC and DA are equal, opposite, and act along the axis of the coil … The forces on arms AB and CD are F1 and F2. They too are equal and opposite, with magnitude, F1 = F2 = I b B”