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JEE Main 2021 (18 Mar, Shift 1) · AC Basics: Peak, RMS & Average Values

AC Basics: Peak, RMS & Average Values question from JEE Main 2021 (18 Mar, Shift 1)

Q31JEE Main 2021 · 18 MAR · SHIFT 1Easy

AC Basics: Peak, RMS & Average Values

An AC source rated 220 V, 50 Hz is connected to a resistor. The time taken by the current to change from its maximum to the rms value is:

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Answer: (a)

  1. Take I=I0cos⁡ωtI = I_0\cos\omega t (maximum at t=0t = 0).
  2. rms value: I0cos⁡ωt=I02⇒ωt=π4I_0\cos\omega t = \frac{I_0}{\sqrt{2}} \Rightarrow \omega t = \frac{\pi}{4}, i.e. t=T8t = \frac{T}{8}.
  3. T=150=20T = \frac{1}{50} = 20 ms, so t=208=2.5t = \frac{20}{8} = 2.5 ms
  4. So the answer is (a) 2.5 ms.
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