Half-wave rectifier (ideal diode): Given an input of v(t) = 20 sin(ωt) volts, determine the average (DC) value and the root-mean-square (rms) value of the output voltage.

Difficulty: Easy

Correct Answer: V_avg ≈ 6.37 V and V_rms = 10 V

Explanation:


Introduction / Context:
Half-wave rectifiers pass only one half-cycle of a sinusoid. For an ideal diode, the negative half is completely blocked, leading to standard formulae for the average (DC) and rms output values. This problem reinforces those results for a specific amplitude.


Given Data / Assumptions:

  • Input: v(t) = V_m sin(ωt) with V_m = 20 V.
  • Ideal diode (no drop), pure half-wave rectification.
  • Output taken across the load directly.


Concept / Approach:

For an ideal half-wave rectifier: V_avg = V_m/π and V_rms = V_m/2. These come from integrating the rectified waveform over a full period, remembering that the second half of the cycle is zero.


Step-by-Step Solution:

V_avg = V_m / π = 20 / π ≈ 6.366 V → ≈ 6.37 V.V_rms = V_m / 2 = 20 / 2 = 10 V.


Verification / Alternative check:

Compute rms from definition: V_rms^2 = (1/2π) ∫0→π (V_m sinθ)^2 dθ = V_m^2/4 → V_rms = V_m/2, confirming 10 V.


Why Other Options Are Wrong:

  • Options listing 5 V for average or rms contradict standard half-wave results.
  • Average of 10 V implies full-wave or different amplitude.
  • Values like 14.14 V correspond to V_m/√2 of an unrectified sine, not a half-wave output.


Common Pitfalls:

  • Forgetting the average is over the full period, not just the conducting half.
  • Confusing full-wave with half-wave formulae.


Final Answer:

V_avg ≈ 6.37 V and V_rms = 10 V

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