Consider the following statements about a current loop placed in a un…

The correct answer is Option (4) → (A) and (C) only

In a uniform field, the forces on opposite sides of a current loop are equal and opposite. They form a couple, and the torque on the loop is \( \vec\tau=\vec m\times\vec B \).

(A) The loop experiences a net force as well as a torque. — False. The forces on the arms add up to zero, so there is a torque but no net force.

(B) The torque on the loop is zero when its magnetic moment is parallel to the field. — True. With \( \vec m \) parallel to \( \vec B \), \( \sin\theta=0 \) and the torque is zero.

(C) When the magnetic moment is antiparallel to the field, the loop is in stable equilibrium. — False. The torque is zero there too, but a small turn produces a torque that turns the loop further. So the equilibrium is unstable.

(D) The SI unit of the magnetic moment of the loop is A m². — True. Since \( m=IA \), its unit is ampere times square metre.

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 torque τ vanishes when m is either parallel or antiparallel to the magnetic field B. …”

Torque on a rectangular current loop in a uniform magnetic field – “… When m and B are parallel the equilibrium is a stable one. Any small rotation of the coil produces a torque which brings it back to its original position. When they are antiparallel, the equilibrium is unstable as any rotation produces a torque which increases with the amount of rotation. …”

Torque on a rectangular current loop in a uniform magnetic field – “… the dimensions of the magnetic moment are [A][L²] and its unit is Am².”