Question
A 220 V A.C. supply is connected between points A and B (Fig.). What will be the potential difference V across the capacitor?

Answer

  1. $220\sqrt{2}\text{V}.$
Solution:
Key concept: Half wave rectifier: When the P-N junction diode rectifies half of the ac wave, it is called half wave rectifier.

  1. During positive half cycle,
Diode → Forward biased
Output signal → obtained
  1. During negative half cycle,
Diode → reverse biased
Output signal → not obtained
  1. Output voltage is obtained across the load resistance RL. It is not constant but pulsating (mixture of ac and dc) in nature.
  2. Average output in one cycle
$\text{I}_\text{dc}=\frac{\text{I}_0}{\pi}\text{ and }\text{V}_\text{dc}=\frac{\text{V}_0}{\pi};\text{I}_0=\frac{\text{V}_0}{\text{r}_\text{f}+\text{R}_\text{I}}$
(rf = forward biased resistance)
  1. r.m.s. output: $\text{I}_\text{rms}=\frac{\text{I}_0}{2},\text{V}_\text{rms}=\frac{\text{V}_0}{2}$
As p-n junction diode will consuct during positive half cycle only, during negative half cycle diode is reverse biased. During this diode will not give any output. So, potential difference across capacitor C = peak voltage of the given AC voltage
$=\text{V}_0=\text{V}_\text{rms}\sqrt{2}=220\sqrt{2}\text{V}$

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