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,$\varphi =\frac{\pi }{2}$,
$I_{rms}=\frac{I_0}{\sqrt{2}}=\frac{5}{\sqrt{2}}$ and
$V_{rms}=\frac{V_0}{\sqrt{2}}=\frac{300}{\sqrt{2}}$
$\therefore$ Power, $P=I_{rms}{V}_{rms}\cos \varphi$
$=\frac{5}{\sqrt{2}}\cdot \frac{300}{\sqrt{2}}\cos \frac{\pi }{2}=0$