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Q.3 Physics · Section A ⭐ 360° Option Elimination Active
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NEET 2024 Physics Question 3 Solution

Topic: Semiconductor Electronics · Official NTA Booklet Code T1
NEET 2024 Physics Question 3: Characteristics of Solar Cells and Reverse Biased Diodes

Question

Consider the following statements A and B and identify the correct answer: A. For a solar-cell, the I-V characteristics lies in the IV quadrant of the given graph. B. In a reverse biased pn junction diode, the current measured in (μA), is due to majority charge carriers.

✓
Verified Against NTA Final Answer Key
Option (3) : A is correct but B is incorrect.
📚 Semiconductor Electronics Easy
📋 Given Parameters & Problem Setup
Statement A For a solar-cell, the I-V characteristics lies in the IV quadrant of the given graph.
Statement B In a reverse biased pn junction diode, the current measured in (μA), is due to majority charge carriers.
⚡

The 30-Second Exam Hall Shortcut: ⚡ Photocell & Reverse Bias 10-Second Recall

⏱️ Save ~40 seconds

Solar cell generates electrical power (delivers current at positive voltage -> IV quadrant); Reverse bias current is due to MINORITY carriers!

1 A solar cell does not consume power; it delivers power to a load, meaning when voltage is positive, current is drawn OUT of the cell (I < 0), placing its characteristic strictly in the 4th quadrant -> Statement A is CORRECT.
2 In reverse bias, the external field opposes majority carrier diffusion and sweeps MINORITY carriers across the junction, generating the tiny reverse saturation current in μA -> Statement B is INCORRECT.
3 Thus, A is correct but B is incorrect -> Pick Option (3) immediately!
🛡️
Why You Can 100% Trust This Shortcut: NCERT Physics · Semiconductor Electronics (Solar cell IV-characteristics and reverse bias minority carrier drift).
📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Analysis of Statement A (Solar Cell IV Characteristics)

A solar cell is a p-n junction diode operated without any external bias voltage. When sunlight illuminates the depletion region, electron-hole pairs are photogenerated. The internal junction electric field sweeps electrons to the n-side and holes to the p-side, setting up a photo-voltage. When connected across a load, it supplies current. Because it supplies power rather than drawing power, the current flows out of the positive terminal, resulting in a negative current convention for positive voltage. Hence, the I-V curve lies in the IV quadrant.

Pdelivered=V⋅I<0  ⟹  (V>0,I<0)∈Quadrant IVP_{delivered} = V \cdot I < 0 \implies (V > 0, I < 0) \in \text{Quadrant IV}
Step 2

Analysis of Statement B (Reverse Biased Diode Current)

When a p-n junction is reverse biased (p-side connected to negative terminal, n-side to positive terminal), the potential barrier height increases, completely blocking majority carriers from diffusing across the junction. The only current that flows is the reverse saturation current (order of microamperes, μA), which is caused solely by the drift of thermally generated MINORITY carriers (electrons from p-side and holes from n-side) swept across the depletion layer by the junction field. Therefore, the reverse current is due to minority carriers, not majority carriers.

Ireverse=I0∝density of minority carriersI_{reverse} = I_0 \propto \text{density of minority carriers}
Step 3

Verdict Synthesis

Statement A is completely correct. Statement B falsely claims the reverse current is due to majority carriers. Therefore, "A is correct but B is incorrect", matching Option (3).

Statement A: True,Statement B: False\text{Statement A: True}, \quad \text{Statement B: False}
⭐

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:

Incorrect because Statement B is false.

⚠️
Student Fallacy (Why candidates pick this trap): Believing that majority carriers flow in reverse bias.
2 (2)
✗ Incorrect
Verdict & Scientific Reason:

Incorrect because Statement A is true.

⚠️
Student Fallacy (Why candidates pick this trap): Thinking solar cells operate in the 1st quadrant like normal forward-biased LEDs.
3 (3)
✓ 100% Correct
Verdict & Scientific Reason:

Solar cell characteristics reside in the IV quadrant; reverse bias current is mediated by minority carriers.

💡
Why this is airtight: None; scientifically accurate.
4 (4)
✗ Incorrect
Verdict & Scientific Reason:

Completely inverted verdict for both statements.

⚠️
Student Fallacy (Why candidates pick this trap): Total misconception of both devices.
⚠️

NTA Trap Alert: Solar Cell vs Photodiode Operating Quadrants

Students confuse a photodiode (operated in 3rd quadrant under external reverse bias) with a solar cell (operated in 4th quadrant without external bias).

🛡️ How to avoid the -1 mark: Remember: Solar cells generate power without external bias -> Quadrant IV. Photodiodes detect light under reverse bias -> Quadrant III.
📖

Core NEET Syllabus Standard

Physics Core Modern Physics · Semiconductor Electronics: Materials, Devices and Simple Circuits Standard Benchmark
Core Scientific Principle Tested:

"Solar cells supply power and their I-V curve lies in the fourth quadrant; reverse saturation current in a p-n junction is governed entirely by minority carrier drift."

Syllabus Focus: p-n Junction Diode Applications and Solar Cells
✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗
Solar Shines in Quadrant Four; Reverse Current is Minority Lore!

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