Four wires each of length 2 m are bent in the form of four loops P, Q, R and S as shown below. They are suspended in a uniform magnetic field. Each loop carries the same current. Identify the correct statement.

1. torque on loop P is maximum.
2. torque on loop Q is maximum.
3. torque on loop R is maximum.
4. torque on loop S is maximum.

torque on loop S is maximum.

Reason — When a current-carrying loop is placed in a uniform magnetic field, the torque acting on it depends upon :

• Strength of the magnetic field
• Area of the loop
• Magnitude of current flowing
• Orientation of the loop relative to the magnetic field

Here, all four loops are placed with same orientation with same current and magnetic field so now the torque is directly proportional to the area (A) enclosed by the loop.

All four loops are made from wires of the same length (2 m), but different shapes enclose different areas. For a given perimeter, a circular loop encloses the maximum area.

Since loop S is circular, it has the largest area among P, Q, R, and S, and therefore experiences the maximum torque.