A current carrying loop is placed in a uniform magnetic field in four different orientations I, II, III and IV as shown in figure. Arrange them in decreasing order of potential energy.

Step-by-step solution

As we know that, potential energy of a magnet in a magnetic field aligned U & =- m B & =-m B aligned where, m= magnetic dipole moment of the magnet B= magnetic field Case I =180^ U₁=-m B 180^ =m B [ 180^ =-1 ] Case II =90^ U₂=0 [ 90^ =0 ] Case III is acute angle aligned & & (0,90^ ) & & = positive Thus, & U₃ & = negative aligned Case IV is obtuse array rlrl & & (90^ , 180^ ) & (0,-1) array Thus, U₄= positive Therefore, decreasing order of P E is I IV II III