Question:
An $\mathrm{AC}$ source rated $220 \mathrm{~V}, 50 \mathrm{~Hz}$ is connected to a resistor. The time taken
by the current to change from its maximum to the rms value is:
Correct Option: 1
Solution:
(1)
$\mathrm{i}=\mathrm{i}_{0} \cos (\omega t)$
$\mathrm{i}=\mathrm{i}_{0}$ at $\mathrm{t}=0$
$\mathrm{i}=\frac{\mathrm{i}_{0}}{\sqrt{2}}$ at $\omega \mathrm{t}=\frac{\pi}{4}$
$\mathrm{t}=\frac{\pi}{4 \omega}=\frac{\pi}{4(2 \pi \mathrm{f})}=\frac{1}{8 \mathrm{f}}$
$\mathrm{t}=\frac{1}{400}=2.5 \mathrm{~ms}$
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