Electro Magnetic Induction And Alternating Currents Question 77
Question: The potential difference V and the current i flowing through an instrument in an ac circuit of frequency f are given by $ V=5\cos \omega t $ volts and I = 2 sin wt amperes (where w = 2pf). The power dissipated in the instrument is [CPMT 1977, 80; MP PET 1999]
Options:
A) Zero
B) 10 W
C) 5 W
D) 2.5 W
Show Answer
Answer:
Correct Answer: A
Solution:
$ V=5\cos \omega t=5\sin ( \omega t+\frac{\pi }{2} ) $
and $ i=2\sin \omega t $ Power $ ={V_{r.m.s.}}\times {i_{r.m.s.}}\times \cos \varphi $ = 0
(Since $ \varphi =\frac{\pi }{2} $ ,
therefore $ \cos \varphi =\cos \frac{\pi }{2}=0 $ )
