2 Marks Questions

Question 12 Marks

What is wattless current.

Answer

If there is no power expenditure when current flows in an alternating circuit, then the current in the circuit is called wattless current. This is possible when the value of power coefficient is zero.
i.e., $\Psi=0$ or $\Psi=\pi/2$

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Question 22 Marks

The equation of an A.C. is $I = 20 sin 200 \pi t$. Find out the frequency, peak value and rms value of the current.

Answer

Given equation $I = 20 sin 200 \pi t$ when compared with equation $I=I_{0} sin \omega t$, we get $I_{0}=20$ A and $\omega=200~\pi$
Hence $\omega=200~\pi$
$\Rightarrow 2\pi f=200~\pi$
Frequency $f=100~Hz.$
Peak value of current $=I_{0}=20~A$
RMS value of current:
$I_{rms}=\frac{I_{0}}{\sqrt{2}}=\frac{20A}{\sqrt{2}}=10\sqrt{2}A$

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