Get the potential energy of a current-carrying loop in a B field that has a uniform over the face area of the loop. The work an external agent would have to perform to change the orientation of a loop in the B field, originally at rest with the loop plane perpendicular to the field, is stored as PE of the loop-field system. Allow an angle of 90 degrees to serve as a reference position for U=0 and discover the expression for U(θ).