Q.20 Physics ⭐ 360° Option Elimination Active

NEET 2023 Physics Question 20 Solution

Topic: Semiconductor Electronics: Materials, Devices and Simple Circuits · Official NTA Booklet Code G5

Question

A full wave rectifier circuit consists of two p-n junction diodes, a centre-tapped transformer, capacitor and a load resistance. Which of these components remove the ac ripple from the rectified output?

✓

Verified Against NTA Final Answer Key

Option (4) : Capacitor

📚 Semiconductor Electronics: Materials, Devices and Simple Circuits Easy

📋 Given Parameters & Problem Setup

Circuit Full wave rectifier with centre-tapped transformer, 2 diodes, capacitor, and load resistor

Target Action Component that removes the AC ripple from rectified output

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The 30-Second Exam Hall Shortcut: ⚡ Filter Circuit Component Memory Hook

⏱️ Save ~30 seconds

A rectifier converts AC to pulsating DC; to smooth/remove the AC ripple, a CAPACITOR filter (or inductor choke) is used!

1 Diodes perform rectification (convert bidirectional AC into pulsating unidirectional DC).

2 The output across the diodes contains both a DC component and an unwanted AC ripple.

3 To remove/filter this AC ripple, a capacitor is connected in parallel with the load (or an inductor in series).

4 The capacitor offers low reactance to AC (X_C = 1/ωC) bypassing it to ground, while blocking DC and forcing steady DC through the load.

5 Therefore, the Capacitor removes the AC ripple. Instant Option (4)!

🛡️

Why You Can 100% Trust This Shortcut: NCERT Physics · Semiconductor Electronics (Filter circuits: Capacitor connected in parallel with load resistance removes the AC ripple).

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Nature of Rectified Output

The output of a full-wave rectifier consisting of two p-n junction diodes and a center-tapped transformer is unidirectional but pulsates periodically with twice the input frequency (ripple frequency = 2f). This output consists of a desired DC component superimposed with unwanted AC ripple harmonics.

Step 2

Role of Capacitor as a Filter

To obtain a steady DC voltage without fluctuations, a filter circuit is employed. A capacitor filter is connected in parallel with the load resistance R_L. Its capacitive reactance is frequency-dependent:

X_C = \frac{1}{2\pi f_{\text{ripple}} C}

Step 3

Bypass Mechanism

For the high-frequency AC ripple components, X_C is very low, providing an easy low-impedance bypass path. For DC (f = 0), X_C → ∞, meaning zero DC current leaks through the capacitor, forcing steady DC voltage across the load resistance R_L:

X_{C,\text{DC}} = \infty, \qquad X_{C,\text{AC}} \ll R_L

⭐

360° Option Elimination Engine Key Feature

Diagnose every choice: Know exactly why the right option works and why distractors fail.

4-Option Deep Scan

1 (1)

✗ Incorrect

Verdict & Scientific Reason:

The load resistance consumes output power and dissipates current; it has no filtering capability.

⚠️

Student Fallacy (Why candidates pick this trap): Candidate confused the output load terminal with the filtering element.

2 (2)

✗ Incorrect

Verdict & Scientific Reason:

The transformer steps down AC voltage and provides out-of-phase AC signals for alternating conduction.

⚠️

Student Fallacy (Why candidates pick this trap): Candidate confused voltage transformation with ripple suppression.

3 (3)

✗ Incorrect

Verdict & Scientific Reason:

Diodes perform rectification (converting AC into pulsating DC); they create the ripple, not filter it.

⚠️

Student Fallacy (Why candidates pick this trap): Candidate confused the rectification stage with the filtering stage.

4 (4)

✓ 100% Correct

Verdict & Scientific Reason:

Accurate component: capacitor acts as a low-pass filter, smoothing pulsating voltage and removing AC ripple.

💡

Why this is airtight: None. Candidate correctly identified the capacitor filter circuit.

⚠️

NTA Trap Alert: Confusing Rectification (Diodes) with Filtering (Capacitor)

Many candidates see "remove AC" and think of the diodes. Diodes remove the negative half-cycles to make current unidirectional, but the capacitor removes the ripple to make it smooth DC.

🛡️ How to avoid the -1 mark: Diodes = Rectifier. Capacitor = Filter (Ripple Remover).

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Core NEET Syllabus Standard

National Eligibility cum Entrance Test (NEET UG) · Semiconductor Electronics: Materials, Devices and Simple Circuits Standard Benchmark

Core Scientific Principle Tested:

"Capacitor connected in parallel across load resistance charges during peak voltage and discharges through load during dips, removing AC ripple."

Syllabus Focus: Full Wave Rectifier and Capacitor Filter Circuits

Preserved in Rationalized Curriculum Syllabus & Academic Standards ↗

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NEET 2023 Physics Question 20 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Filter Circuit Component Memory Hook

Step-by-Step Rigorous Workflow & Mathematical Proof

Nature of Rectified Output

Role of Capacitor as a Filter

Bypass Mechanism

360° Option Elimination Engine Key Feature

NTA Trap Alert: Confusing Rectification (Diodes) with Filtering (Capacitor)

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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