Problem 1 A rectangular coil of /turns and of length a and width bis rotated at frequency fin a uniform magnetic field of magnitude 8, as indicated in the figure. The coil is connected to co-rotating cylinders, against which metal brushes slide to make contact. The emf induced in the coil is given (as a function of time () by E=2ufNabBsin(2uft]=Eosin(2nift) This is the principle of the commercial alternating-current generator. What value of Nab gives an emf with co = 218 V when the loop is rotated at 66.5 rew/'s in a uniform magnetic field of 0.413 T? Sliding contacts XXXXXXXXXXX R X XXXXXXXXXXX