Consider the following statements about the filters used with a rectifier:
(A) A filter capacitor gets charged while the voltage across it is rising.
(B) A filter inductor is connected in parallel with the load \(R_L\).
(C) The rate of fall of the voltage across the filter capacitor depends inversely on the product \(CR_L\).
(D) Capacitor input filters use small capacitors.
Which of the above statements are incorrect?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (B) and (D) only
A filter removes most of the ac ripple from the rectified output. The capacitor is placed across the load, and an inductor is placed in series with the load.
(A) A filter capacitor gets charged while the voltage across it is rising. — Correct statement. As the rectified voltage rises towards the peak, charge flows onto the capacitor.
(B) A filter inductor is connected in parallel with the load \(R_L\). — Incorrect statement. An inductor used as a filter is connected in series with \( R_L \).
(C) The rate of fall of the voltage across the filter capacitor depends inversely on the product \(CR_L\). — Correct statement. The capacitor discharges through the load. A larger \( CR_L \), the time constant, gives a slower fall.
(D) Capacitor input filters use small capacitors. — Incorrect statement. A large time constant needs a large value of C. So these filters use large capacitors.
NCERT (2026-27):
Application of Junction Diode as a Rectifier – “Now we shall discuss the role of capacitor in filtering. When the voltage across the capacitor is rising, it gets charged. …”
Application of Junction Diode as a Rectifier – “… One can also use an inductor in series with RL for the same purpose. …”
Application of Junction Diode as a Rectifier – “… The rate of fall of the voltage across the capacitor depends inversely upon the product of capacitance C and the effective resistance RL used in the circuit and is called the time constant. …”
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. …”