CONCEPT: As the current-carrying conductor experiences a force when placed in a magnetic field, each side of a current-carrying rectangular coil experiences a force in a magnetic field. In the present section, we shall see in what way the rectangular loop carrying current is influenced by a magnetic field. [ alt="F1 J.K Madhu 13.05.20 D12" src="//storage.googleapis.com/tb-img/production/20/05/F1_J.K_Madhu_13.05.20_D12.png" style="width: 419px; height: 289px;"> Consider a rectangular coil of length l and breadth b carrying a current I placed in a uniform magnetic field B. θ, be the angle between the plane of the rectangular coil and the magnetic field. Force acting on the rectangular loop: F = I L B sinθ, where F is force, I = current, L = distance from the axis, B = strength of the magnetic field, θ = angle between the plane of the rectangular coil and the magnetic field. Acting on the upper and lower sides are equal and opposite along the same line of action, they cancel each other. As the force acting on the sides QR and SP are equal and opposite along different lines of action they constitute a couple. So, the torque acting on the loop is, T = force × arm of the couple T = B I L × b Sinθ = B I A Sinθ T = B I A Sinθ EXPLANATION: The torque acting on the rectangular loop is T = B I A sin θ. So option 2 is correct.