Question

What is power dissipation in an $ a.c. $ circuit in which voltage and current are given by $ V = 300\, \sin\,(\omega t + \pi / 2) $ , $ I = 5\, \sin\,\omega t $ ?

• A. zero
• B. 300 units
• C. 150 units
• D. 75 units

Answer 1

Answer: (A)

Given, $V = 300\, \sin\,(\omega t + \frac{\pi}{2})$,
$ I = 5\,\sin \,\omega t$
Here,$ \phi = \frac{\pi}{2}$,
$ I_{rms} = \frac{I_0}{\sqrt{2}} = \frac{5}{\sqrt{2}}$ and
$ V_{rms} = \frac{V_0}{\sqrt{2}} = \frac{300}{\sqrt{2}}$
$\therefore $ Power, $P = I_{rms}V_{rms} \,\cos\,\phi $
$= \frac{5}{\sqrt{2}} \cdot \frac{300}{\sqrt{2}} \,\cos \frac{\pi}{2} =0$