Rankers Physics

Alternating Current: Practice Problem & Solution

35. The instantaneous values of alternating current and voltages in a circuit are given as $i = frac{1}{sqrt{2}} sin(100pi t)$ ampere, $e = frac{1}{sqrt{2}} sin(100pi t + frac{pi}{3})$. The average power in watts consumed in the circuit is: (2012 Mains)
$1/4$
$\sqrt{3}/4$
$1/2$
$1/8$

Solution Explained:

To solve this problem, we apply the core principles of Alternating Current. Understanding the underlying formula is key to arriving at the correct answer below:

$V_{rms} = \frac{V_0}{\sqrt{2}} = \frac{1/\sqrt{2}}{\sqrt{2}} = \frac{1}{2} V$ and $I_{rms} = \frac{I_0}{\sqrt{2}} = \frac{1/\sqrt{2}}{\sqrt{2}} = \frac{1}{2} A$.
The phase difference between voltage and current is $\phi = \frac{\pi}{3}$.
Average power $P = V_{rms} I_{rms} \cos\phi = \frac{1}{2} \times \frac{1}{2} \times \cos(\frac{\pi}{3})$.
$P = \frac{1}{4} \times \frac{1}{2} = \frac{1}{8} W$.

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