Semiconductor Electronics: Materials, Devices and Simple CircuitsNEET MCQs with solutions
Semiconductor Electronics covers intrinsic and extrinsic semiconductors, p-n junction diode, LED, photodiode, solar cell, Zener diode, transistor (npn, pnp) and logic gates. NEET tests p-n junction behaviour (forward/reverse bias), transistor as amplifier/switch, logic gate truth tables and semiconductor band theory.
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- 12 Physics
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- 24 questions
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- 746 questions
- ELITE questions
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- NCERT topics
- 17
Practise 24 questions
Tap an option to check it. Questions from every NCERT topic in this chapter, from easy to hard.
Q1Grand Test
In an intrinsic semiconductor at absolute zero temperature (0 K), which of the following correctly describes its electrical behaviour?
Not quite — the answer is A.
At 0 K, all electrons are tightly bound in the valence band and the conduction band is completely empty, making the material a perfect insulator. Options C and D are wrong because intrinsic semiconductors have no dopants to create n-type or p-type behaviour.
Q2Energy Band Theory
Which energy band contains the energy levels occupied by the valence electrons of a solid?
Not quite — the answer is B.
The valence band contains the energy levels of valence electrons. The conduction band lies above it and contains electrons free for conduction. The forbidden band has no allowed states.
Q3Mixed Revision
In a common-emitter NPN amplifier, the input signal is applied between the base and emitter. The output signal at the collector is:
Not quite — the answer is B.
When IB increases, IC increases, voltage drop ICRC increases, and VC=VCC-ICRC decreases. So output is inverted — 180° out of phase. This is the defining CE amplifier phase property.
Q4Classification of Solids
Choose the INCORRECT statement regarding conductors, semiconductors and insulators.
Not quite — the answer is C.
Statement C is false. Increasing temperature generates more electron-hole pairs in a semiconductor, raising conductivity and lowering resistivity. Statement D (conductivity increases) is the correct counterpart.
Q5Intrinsic Semiconductors
In an intrinsic semiconductor at a given temperature, the number of free electrons is:
Not quite — the answer is B.
In an intrinsic semiconductor, electron-hole pairs are generated thermally in pairs. Each excited electron leaves exactly one hole. Therefore ne = nh = ni at all temperatures above 0 K.
Q6p-n Junction Formation
When a p-type and n-type semiconductor are joined, the initial movement of majority carriers across the junction occurs mainly because of:
Not quite — the answer is C.
Hole concentration is high on p-side, electron concentration high on n-side. This gradient drives diffusion — holes to n-side, electrons to p-side. No external agency is needed; concentration gradient alone initiates carrier movement.
Q7Forward Bias & Reverse Bias
A p-n junction diode is said to be forward biased when:
Not quite — the answer is B.
In forward bias, p-side connects to the positive terminal and n-side to the negative terminal. The applied field opposes the built-in junction field, reducing depletion width and allowing majority-carrier diffusion across the junction.
Q8Rectifiers
In a full-wave rectifier operating from a 50 Hz AC supply, the fundamental frequency of the rectified output is:
Not quite — the answer is A.
FWR produces pulses in both half-cycles so f_out = 2f = 2x50 = 100 Hz. Option B is the input frequency, a common confusion. Option D is f/√2, which has no physical basis here.
Q9Transistor as a Switch
A transistor is used as a switch in common-emitter configuration. Which two regions of operation correspond to the OFF and ON states respectively?
Not quite — the answer is B.
Cut-off gives I_C ≈ 0 and acts as an open switch (OFF). Saturation drives both junctions forward biased, giving strong conduction (ON). The active region is used for amplification, not ideal switching.
Q10Boolean Logic & Universal Gates
A Boolean circuit has output Y = (A+B)-bar. Which pair of gates directly implements this function?
Not quite — the answer is C.
Y = (A+B)-bar requires first computing A+B via OR, then inverting via NOT. Option B gives ((A+B)-bar)-bar = A+B, which is OR — double inversion cancels the complement, giving the wrong function.
Q11Introduction to Semiconductors
As the temperature increases, the electrical resistance of a semiconductor generally:
Not quite — the answer is B.
Increasing temperature generates more thermally excited electron-hole pairs. Higher carrier concentration raises conductivity, so resistance decreases. Option D describes a metal near a phase transition, not a semiconductor.
Q12Junction Transistor (Construction & Working)
In an n-p-n transistor operating in the active region, the collector is at a higher potential than the base and emitter. Which bias condition does this satisfy?
Not quite — the answer is B.
In active mode, the emitter-base junction is forward biased (permits carrier injection) and the collector-base junction is reverse biased (sweeps injected carriers to the collector). Option A exactly reverses the two bias conditions — the most common error.
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Get RankUp on Google PlayQ13Logic Gates
A two-input NAND gate has inputs A = 1 and B = 1. Its output is:
Not quite — the answer is D.
NAND gives Y = (AB)-bar. For A=B=1, AB=1, so Y = 1-bar = 0. Output is LOW only for this all-HIGH input combination. Option A is the most common error — students confuse NAND with AND for the 11 input.
Q14Special Purpose Diodes (Zener, LED, Photodiode, Solar Cell)
A Zener diode is specifically designed to operate in which region when used as a voltage regulator?
Not quite — the answer is A.
A Zener diode is heavily doped and designed to operate in the reverse breakdown region, where its voltage remains nearly constant over the useful current range, enabling voltage regulation.
Q15Transistor Characteristics & Current Gain (α, β)
A transistor has a common-base current gain α = 0.96. The common-emitter current gain β is:
Not quite — the answer is C.
β = α/(1−α) = 0.96/0.04 = 24. Trap: option A (β=6) arises from wrongly computing 0.96/0.16, confusing (1−α) with (1−α²). Memorise β = α/(1−α).
Q16Extrinsic Semiconductors (n-type & p-type)
When a pure semiconductor is doped with a pentavalent impurity, the resulting semiconductor is:
Not quite — the answer is C.
A pentavalent impurity donates its fifth valence electron after four participate in covalent bonds. This raises electron concentration above hole concentration, forming an n-type semiconductor.
Q17Diode Characteristics
In a p-n junction diode, an increase in temperature due to heating affects:
Not quite — the answer is D.
Heating increases thermally generated electron-hole pairs, reduces the potential barrier, and shifts the diode characteristic. The entire V-I curve is affected — not just one type of resistance. Options A and B incorrectly limit the effect to one bias direction.
Q18Introduction to Semiconductors
On the basis of electrical conductivity, which material has the smallest resistivity?
Not quite — the answer is C.
Silver is a metallic conductor with resistivity ~10⁻⁸ Ω m, the lowest among the options. Germanium and silicon are semiconductors; glass is an insulator with far higher resistivity.
Q19Introduction to Semiconductors
A semiconductor is best described as a material whose electrical conductivity at ordinary conditions is:
Not quite — the answer is C.
Semiconductors have conductivity between conductors (~10⁷ S/m) and insulators (~10⁻¹¹ S/m). Option D is false — metals have far greater conductivity. Option B describes behaviour only at 0 K.
Q20Introduction to Semiconductors
Which statement correctly distinguishes a semiconductor from an ordinary metallic conductor?
Not quite — the answer is A.
Semiconductors have a negative temperature coefficient — resistance decreases on heating due to increased carriers. Metals have a positive temperature coefficient — resistance increases on heating. Option D reverses both signs, a classic student error.
Q21Introduction to Semiconductors
In an intrinsic semiconductor, as temperature is raised from room temperature, which of the following correctly describes the change in mobile carriers and conductivity?
Not quite — the answer is A.
Thermal energy excites valence electrons across the forbidden gap, generating electron-hole pairs. More carriers directly increase conductivity — both rise together. Options C and D are internally inconsistent with semiconductor physics.
Q22Introduction to Semiconductors
Which statement correctly compares the resistivity of a semiconductor with that of silver at room temperature?
Not quite — the answer is A.
Metals such as silver have resistivity ~10⁻⁸ Ω m; silicon has resistivity ~10² Ω m — roughly 10 orders of magnitude higher. Option D is false — semiconductor resistivity is strongly temperature dependent.
Q23Introduction to Semiconductors
Consider the following statements about semiconductors: I. Conductivity generally increases with temperature. II. Resistance generally decreases with temperature. III. Conductivity is always greater than metallic conductivity. IV. Silicon is a commonly used semiconductor. How many of the above statements are correct?
Not quite — the answer is D.
Statements I, II and IV are correct. III is false — metals have conductivity many orders of magnitude higher than semiconductors at room temperature. Students confuse higher conductivity with higher carrier sensitivity.
Q24Introduction to Semiconductors
Which of the following statements about semiconductor resistivity is correct?
Not quite — the answer is C.
Semiconductor resistivity decreases with increasing temperature due to more thermally generated carriers. It never reaches zero — it asymptotically decreases. Option D is the most common trap: students confuse this with superconductivity.
ELITE question · AIR under 50 level
This chapter has 265 ELITE questions for students aiming at the very top. They are only in the app.
Unlock ELITE questions in the appKey Semiconductor Concepts
Quick revision: most questions in this chapter test these facts.
| Concept | Key Fact |
|---|---|
| n-type semiconductor | Doped with pentavalent (P, As); majority carriers = electrons |
| p-type semiconductor | Doped with trivalent (B, Al); majority carriers = holes |
| p-n junction | Forward bias: current flows (low resistance); Reverse bias: no current (high resistance, only leakage) |
| Zener diode | Reverse bias breakdown at fixed voltage; used as voltage regulator |
| Transistor | npn/pnp; CE config: current gain β = I_C/I_B; used as amplifier and switch |
| Logic gates | AND: A·B; OR: A+B; NOT: Ā; NAND: universal gate; NOR: universal gate |
What the app covers in this chapter
746 questions in total, each with a detailed explanation.
| Grand Test | 80 |
| Energy Band Theory | 60 |
| Mixed Revision | 58 |
| Classification of Solids | 41 |
| Intrinsic Semiconductors | 40 |
| p-n Junction Formation | 40 |
| Forward Bias & Reverse Bias | 40 |
| Rectifiers | 40 |
| Transistor as a Switch | 40 |
| Boolean Logic & Universal Gates | 40 |
| Introduction to Semiconductors | 39 |
| Junction Transistor (Construction & Working) | 39 |
| Logic Gates | 39 |
| Special Purpose Diodes (Zener, LED, Photodiode, Solar Cell) | 38 |
| Transistor Characteristics & Current Gain (α, β) | 38 |
| Extrinsic Semiconductors (n-type & p-type) | 37 |
| Diode Characteristics | 37 |
Questions students ask
Is Semiconductor Electronics important for NEET?
Yes — p-n junction, transistor working, logic gates and semiconductor types are tested every year. Both conceptual and circuit-based questions appear.
Which topics should I revise first?
Focus on n-type vs p-type semiconductors, p-n junction in forward/reverse bias, Zener diode as voltage regulator, transistor CE amplifier (current gain β), and truth tables of all logic gates including NAND/NOR as universal gates.
How many questions from this chapter are on RankUp?
The RankUp app has 746 questions on Semiconductor Electronics: Materials, Devices and Simple Circuits, including 265 ELITE questions. Every question has a detailed explanation.
