In a full wave rectifier, the output voltage obtained is in the shape of pulsating half sinusoids which are unidirectional but not steady. To get a steady d.c. output
(A) An inductor can be used in series with the load resistor
(B) A capacitor of high value of capacitance can be used in parallel with the load resistor
(C) A capacitor of low capacitance can be used in series with the load resistor
(D) Only load resistor is enough to filter out the pulses and convert them to d.c.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A) and (B) only
The rectifier output is a d.c. part plus an a.c. ripple. A filter must pass the d.c. part to the load and keep the ripple away from it.
(A) An inductor can be used in series with the load resistor — Correct. An inductor opposes any change in current: it offers no opposition to the d.c. part but a large reactance \( \omega L \) to the ripple, so the load current is smoothed.
(B) A capacitor of high value of capacitance can be used in parallel with the load resistor — Correct. The capacitor charges to the peak voltage and, between peaks, discharges slowly through the load; with a large time constant \( RC \) the voltage hardly falls, so the output is nearly steady.
(C) A capacitor of low capacitance can be used in series with the load resistor — Incorrect. A capacitor in series blocks the d.c. part completely, and a small capacitance also has a large reactance, so it removes exactly what we want to keep.
(D) Only load resistor is enough to filter out the pulses and convert them to d.c. — Incorrect. A resistor has no frequency dependence; the voltage across it follows the pulsating input.
NCERT (2026-27):
Application of Junction Diode as a Rectifier – “… To get steady dc output from the pulsating voltage normally a capacitor is connected across the output terminals (parallel to the load RL). One can also use an inductor in series with RL for the same purpose.”
Application of Junction Diode as a Rectifier – “… To make the time constant large value of C should be large. So capacitor input filters use large capacitors.”