Filter Circuits

NCERT explains that the pulsating output of a rectifier still contains a large alternating ripple, which is smoothed using a filter. A shunt capacitor placed across the load charges up rapidly to the peak voltage while the diode conducts, then discharges slowly through the load resistance when the rectified voltage falls, thereby maintaining a more constant voltage between successive peaks. This charging and discharging action fills in the dips and greatly reduces the ripple. The option that it converts input into pulses before rectification is wrong because the capacitor acts after rectification, on the already rectified output. The option that it increases ripple by resonating is wrong because a filter capacitor reduces ripple; it does not resonate destructively at the supply frequency in this configuration. The option that it blocks the direct component is wrong because that describes a coupling capacitor in signal circuits, whereas here the capacitor deliberately supports the DC level. As stated in NCERT Class 12, Chapter 14, a shunt capacitor filter smooths rectified output. A consistency check confirms that a larger capacitance or larger load resistance lengthens the discharge time and further lowers ripple.