PN Junction Important Questions and Topics For IIT JAM 2026 Physics
PN Junction Important Questions are key for IIT JAM 2026 Physics, covering diode equations, biasing, thermal voltage, dynamic resistance, clippers, clampers, and voltage multipliers. Based on PN Junctions PYQs, these questions focus on concepts, exam trends, and accurate problem-solving.
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PN Junction Important Questions form a core part of semiconductor physics and appear repeatedly in competitive exams. For aspirants preparing for IIT JAM 2026, a strong command over PN junction concepts is necessary. Questions from PN junction diodes test conceptual clarity, formula application, and problem-solving ability rather than memory.
In IIT JAM Physics, PN junction questions are often framed from diode equations, biasing conditions, temperature dependence, and waveform-based circuits. Presented here is a complete and exam-oriented information to PN Junction Important Questions, covering theory focus areas, numerical patterns, and PN Junctions PYQs trends relevant for 2025β26 preparation.
PN Junction Important Questions
This section covers carefully selected multiple-choice questions from PN junction theory that reflect the recurring patterns seen in competitive exams. These PN Junction Important Questions are framed to test conceptual clarity, numerical accuracy, and understanding of diode behaviour under different conditions.
Q1. At room temperature (300 K), the thermal voltage VTV_TVTβ of a PN junction diode is approximately:
A. 13 mV
B. 25.8 mV
C. 52 mV
D. 0.7 V
Correct Answer: B
Explanation: Thermal voltage 
.
Q2. The diode current equation for a PN junction under forward bias is:
Correct Answer: C
Q3. For a silicon diode, the ideality factor Ξ·\etaΞ· used in PN Junction Important Questions is:
A. 0.5
B. 1
C. 1.5
D. 2
Correct Answer: D
Q4. In reverse bias condition, a PN junction diode behaves as:
A. Short circuit
B. Voltage source
C. Open circuit
D. Current source
Correct Answer: C
Q5. The saturation current ISI_SISβ of a PN junction diode is typically of the order of:
A. Amperes
B. Milliamperes
C. Microampere or nanoampere
D. Volts
Correct Answer: C
Q6. Which parameter mainly controls the exponential increase of current in a PN junction diode?
A. Junction area
B. Applied forward voltage
C. Series resistance
D. Load resistance
Correct Answer: B
Q7. Dynamic resistance rdr_drdβ of a diode in forward bias is given by:
Correct Answer: C
Q8. Dynamic resistance of a PN junction diode depends on:
A. Applied voltage
B. Forward current
C. Reverse voltage
D. Saturation current only
Correct Answer: B
Q9. If the forward current through a diode increases, its dynamic resistance will:
A. Increase
B. Remain constant
C. Decrease
D. Become infinite
Correct Answer: C
Q10. The forward voltage drop of a silicon PN junction diode is approximately:
A. 0.2 V
B. 0.3 V
C. 0.5 V
D. 0.7 V
Correct Answer: D
Q11. In a clipper circuit, the main function of the PN junction diode is to:
A. Shift the waveform vertically
B. Amplify the signal
C. Limit the voltage level
D. Change frequency
Correct Answer: C
Q12. In a clamper circuit, which of the following remains unchanged?
A. Peak voltage
B. Waveform shape
C. RMS voltage
D. Output polarity
Correct Answer: B
Q13. The peak-to-peak voltage of a waveform in a clamper circuit:
A. Increases
B. Decreases
C. Becomes zero
D. Remains constant
Correct Answer: D
Q14. For an AC input with RMS value VRMSV_{RMS}VRMSβ, the peak voltage is:
Correct Answer: C
Q15. A voltage doubler circuit ideally provides an output equal to:
A. RMS voltage
B. Half of peak voltage
C. Peak voltage
D. Twice the peak voltage
Correct Answer: D
Q16. Temperature increase in a PN junction diode mainly affects:
A. Junction capacitance
B. Saturation current and thermal voltage
C. Forward voltage drop only
D. Series resistance
Correct Answer: B
Q17. In PN Junctions PYQs, most calculation errors occur due to:
A. Wrong unit conversion
B. Ignoring diode bias condition
C. Incorrect diagram
D. Long calculations
Correct Answer: B
Q18. At room temperature, thermal voltage is often approximated as 26 mV instead of 25.8 mV because:
A. It changes the answer significantly
B. Exact value is unknown
C. Minor rounding does not affect exam answers
D. Formula requires rounding
Correct Answer: C
PN Junctions Important Topics
PN junction questions in IIT JAM Physics are not random. They are concentrated around specific theory areas and numerical applications. The table below lists the most important topics from which PN Junction Important Questions are repeatedly asked.
| PN Junctions Important Topics | ||
| Topic Name | Key Focus Area | Exam Relevance |
| PN Junction Formation | Depletion region, built-in potential | Conceptual clarity |
| Forward Bias | Current flow, voltage drop | High |
| Reverse Bias | Open circuit behaviour, saturation current | High |
| Diode Current Equation | Exponential relation of current | Very High |
| Ideality Factor (Ξ·) | Silicon vs germanium diode | High |
| Thermal Voltage (VT) | Temperature dependence | Very High |
| Saturation Current (IS) | Order of magnitude, temperature effect | Moderate |
| Dynamic Resistance (rd) | Relation with forward current | High |
| Clipper Circuits | Voltage limiting action | Moderate |
| Clamper Circuits | Waveform shifting | Moderate |
| Voltage Doubler | Peak voltage multiplication | Low to Moderate |
| RMS to Peak Conversion | AC signal analysis | High |