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A sinusoidal voltage of peak value 220 V is connected to a diode and a resistor R in the circuit shown. If the diode is ideal, the rms voltage across R is ________ V.

Asked in GUJCET 2013 · Output waveforms

Figure: Output waveforms
Answer: (4) 110

Step-by-step solution

Given: Vₘ = 220 V and an ideal diode, so one half of every cycle reaches R unchanged and the other half is blocked completely.

Idea: rms means the square root of the mean of v² taken over a whole period, and the blocked half contributes zero to that mean.

Over the conducting half the mean of v² is (Vₘ²)/2; over the blocked half it is 0.

Averaging across the whole cycle, v² = 1/2 · (Vₘ²)/2 = (Vₘ²)/4.

So Vᵣₘₛ = (Vₘ)/2 = (220)/2 = 110 V, half the peak and not Vₘ/√2.

Why the other options are wrong

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