Physics Electronics PMDC Conceptual Practice
PMDC Verified Question 84 of 494
To effectively smooth out the pulsating output voltage of a rectifier, the filter capacitor must be connected in:
A
Series with the secondary transformer winding
B
Series with the rectifying diode anode
C
Parallel (shunt) across the DC load resistor
D
Antiparallel across the AC mains input terminals
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: Parallel (shunt) across the DC load resistor
Concept:

A smoothing filter capacitor is placed in parallel with the load resistor so it can maintain the load voltage while the rectified supply falls between pulses.

Formula:

$$R_L C \gg T = \frac{1}{f_{\text{ripple}}}$$

Solution:

  • A shunt capacitor charges to peak voltage during conduction and discharges through the high-resistance load during non-conduction intervals.


  • Connecting the capacitor in parallel maintains a relatively constant voltage across the output terminals.


Why other options are incorrect:

  • Option A: A series capacitor blocks DC current entirely.


  • Option B: Placing a capacitor in series with the diode prevents DC load current flow.


  • Option D: Placing a capacitor across AC mains forms a reactive AC load without smoothing the rectified DC output.

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