A rectangular coil of N turns and of length a and width b is rotated at frequenc
ID: 1468515 • Letter: A
Question
A rectangular coil of N turns and of length a and width b is rotated at frequency f in a uniform magnetic field of magnitude B, 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 t) by ? = 2?fNabB sin (2?ft) = ?0 sin (2?ft). This is the principle of the commercial alternating-current generator. What value of Nab gives an emf with ?0 = 248 V when the loop is rotated at 76.8 rev/s in a uniform magnetic field of 0.631 T?
Explanation / Answer
ANS:Given :2fNabB sin (2ft) = 0 sin (2ft).
2fNabB = 0
Nab= 0 /2fB
since,0 = 248 V
f=76.8 rev/s
B = 0.631 T
=3.14
now substituting the above values in Nab= 0 /2fB
we get, Nab= 248/2 X3.14 X76.8 X0.631
= 248 /304.3333824
therefore , Nab =0.8148946