Semiconductor Electronics — Class 12 MCQs with Answers
Class 12 CBSE Physics · Chapter 14
90 practice questions · 30 Easy · 30 Medium · 30 Hard · Updated
Practise the most important Class 12 CBSE Physics questions from Chapter 14, "Semiconductor Electronics". You get 9 timed quizzes made from 90 NCERT-based MCQs, with answers and explanations. The questions are split into 30 Easy, 30 Medium and 30 Hard. Warm up on the basics, then move on to the exam-level questions that set top scorers in CBSE & Maharashtra HSC Board exams, JEE Main, MHT-CET, JEE Advanced and NEET UG apart.
To score well in "Semiconductor Electronics", focus on numericals, derivations and applying concepts. Each MCQ here is timed and uses exam-style marking (+4 correct, −1 wrong, 0 skipped). This trains you to stay accurate under time pressure, as real papers need. Every question has a short explanation, so a wrong answer becomes a quick lesson. It is the fastest way to fix gaps before a test.
Use this chapter for focused revision. Start with the Easy set to check your basics on Semiconductor Electronics, then move to Medium and Hard to practise applying them. Your accuracy, streaks and XP save automatically. This chapter also adds to your overall Class 12 Physics mastery score. 14 sample questions are solved in full below, with the answer and a worked explanation. Sign in free to start practising.
Key concepts: Semiconductor Electronics (Class 12 Physics)
From energy bands to working devices: how band gaps separate conductors, insulators and semiconductors, intrinsic conduction by electrons and holes, doping to make n-type and p-type material, the pn junction with its depletion region and barrier potential, forward and reverse bias, rectification, and the special-purpose diodes.
- Energy bands in solids
- Atomic energy levels broaden into bands when atoms come together, with a forbidden energy gap separating the filled valence band from the empty conduction band.
- Conductors, insulators, semiconductors
- In a conductor the bands overlap; an insulator has a gap above about 3 eV; a semiconductor's gap is small enough for thermal energy to bridge it.
- Band gap
- Silicon's gap is about 1.1 eV and germanium's about 0.7 eV at room temperature. The smaller gap makes germanium the more thermally sensitive of the two.
- Intrinsic semiconductor
- Pure semiconductor in which electrons and holes are created only in pairs by thermal excitation, so their concentrations are exactly equal.
Semiconductor Electronics — important questions & MCQs with answers (Class 12 Physics)
14 solved questions from this chapter's difficulty levels, each with its answer and explanation. The other 76 are timed and scored when you sign in.
- Q1Easy
Pure silicon is an example of which type of material?
A.ConductorB.Intrinsic semiconductor✓ CorrectC.InsulatorD.SuperconductorAnswer: B. Intrinsic semiconductor
Explanation: Band theory: Si has a ~1.1 eV gap, wide enough to resist free conduction like a metal but narrow enough for thermal excitation — the hallmark of an intrinsic semiconductor, not an insulator.
- Q2Easy
The barrier potential of a silicon pn-junction diode is approximately:
A.0.7 V✓ CorrectB.0.3 VC.1.5 VD.5 VAnswer: A. 0.7 V
Explanation: The built-in barrier (knee voltage) of a silicon pn-junction is ≈0.7 V — germanium's is lower at ≈0.3 V, so swapping the two values is the classic slip here.
- Q3Easy
Adding a pentavalent impurity to silicon gives which type of semiconductor?
A.InsulatorB.p-typeC.n-type✓ CorrectD.ConductorAnswer: C. n-type
Explanation: A pentavalent atom (P, As, Sb) has one extra valence electron beyond Si's four bonds — that spare electron becomes a free carrier, so doping creates an n-type semiconductor, not p-type.
- Q4Easy
The barrier potential of a germanium pn-junction diode is approximately:
A.1.1 VB.0.7 VC.0.3 V✓ CorrectD.2 VAnswer: C. 0.3 V
Explanation: Germanium's junction barrier potential is ≈0.3 V, noticeably lower than silicon's ≈0.7 V because Ge's smaller band gap needs less forward voltage to start conducting.
- Q5Easy
The energy band gap of silicon at room temperature is approximately:
A.0 eVB.0.3 eVC.5 eVD.1.1 eV✓ CorrectAnswer: D. 1.1 eV
Explanation: Silicon's energy gap is ≈1.1 eV at room temperature — remember Si is 1.1 eV, Ge is 0.7 eV; mixing the two values is the usual mistake on this fact.
- Q6Easy
The depletion region of a pn-junction contains:
A.Free electronsB.Immobile ions only✓ CorrectC.Free holesD.Both mobile carriersAnswer: B. Immobile ions only
Explanation: Diffusion sweeps mobile electrons and holes out of the junction region, leaving only the fixed donor and acceptor ions behind — that's why the depletion region has no free carriers.
- Q7Medium
In an extrinsic semiconductor at thermal equilibrium, the product of electron and hole concentrations equals:
A.Nᴀ × NᴅB.nᵢC.nᵢ²✓ CorrectD.ZeroAnswer: C. nᵢ²
Explanation: The mass-action law states that in thermal equilibrium the product of electron and hole concentrations is fixed: n·p = nᵢ², independent of doping — not Nᴀ×Nᴅ, which sets net carrier difference instead.
- Q8Medium
A forward-biased pn-junction diode behaves as:
A.A heating element onlyB.An open circuitC.A high resistance pathD.A low resistance path✓ CorrectAnswer: D. A low resistance path
Explanation: Forward bias narrows the depletion region and lowers the barrier, so majority carriers flow easily — the diode behaves like a low resistance path, not an open circuit or heater.
- Q9Medium
In a pure (intrinsic) semiconductor, the Fermi level lies approximately:
A.In the conduction bandB.Near the middle of the band gap✓ CorrectC.In the valence bandD.Above the conduction bandAnswer: B. Near the middle of the band gap
Explanation: With equal numbers of electrons and holes, the Fermi level sits roughly midway between the valence and conduction bands in an intrinsic semiconductor.
- Q10Medium
A Zener diode is most commonly used as:
A.Voltage regulator✓ CorrectB.AmplifierC.OscillatorD.Switch onlyAnswer: A. Voltage regulator
Explanation: In reverse breakdown, a Zener diode's voltage stays nearly constant even as the current through it changes substantially — this stability is exploited to build voltage regulators.
- Q11Medium
In an n-type semiconductor, the Fermi level lies:
A.Outside the band gapB.Closer to the valence bandC.At mid gapD.Closer to the conduction band✓ CorrectAnswer: D. Closer to the conduction band
Explanation: Excess conduction electrons from donor doping raise the electron occupation probability near the conduction band, so the Fermi level shifts up, closer to Eᴄ.
- Q12Hard
In a metallic conductor, the valence and conduction bands:
A.Are perfectly insulated from each otherB.Are widely separatedC.Overlap completely✓ CorrectD.Are both emptyAnswer: C. Overlap completely
Explanation: In a metallic conductor the valence and conduction bands overlap completely, so electrons need essentially zero extra energy to enter the conduction band, unlike the finite gap in a semiconductor.
- Q13Hard
A bipolar junction transistor (BJT) consists of how many terminals?
A.FiveB.TwoC.FourD.Three (emitter, base, collector)✓ CorrectAnswer: D. Three (emitter, base, collector)
Explanation: A bipolar junction transistor has three doped regions — emitter, base, and collector — each brought out as a separate terminal, giving three terminals in total, not two or four.
- Q14Hard
In an n-type Si sample, nₑ = 5 × 10²² m⁻³. If nᵢ = 1.5 × 10¹⁶ m⁻³, the hole concentration is approximately:
A.4.5 × 10⁹ m⁻³✓ CorrectB.4.5 × 10¹⁵ m⁻³C.1.5 × 10¹⁶ m⁻³D.5 × 10²² m⁻³Answer: A. 4.5 × 10⁹ m⁻³
Explanation: Mass-action law: p = nᵢ²/n = (1.5×10¹⁶)²/(5×10²²) = 2.25×10³²/5×10²² ≈ 4.5×10⁹ m⁻³ — squaring nᵢ before dividing is the step most often skipped.
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Start this chapter free →Semiconductor Electronics — FAQs
What are the key concepts in Class 12 Physics Semiconductor Electronics?+
From energy bands to working devices: how band gaps separate conductors, insulators and semiconductors, intrinsic conduction by electrons and holes, doping to make n-type and p-type material, the pn junction with its depletion region and barrier potential, forward and reverse bias, rectification, and the special-purpose diodes. Key ideas include Energy bands in solids, Conductors, insulators, semiconductors, Band gap, Intrinsic semiconductor.
What does Class 12 Physics Chapter 14 (Semiconductor Electronics) cover on XamBaaz?+
It has 90 NCERT-based MCQs on "Semiconductor Electronics": 30 Easy, 30 Medium and 30 Hard. Together they make 9 timed quizzes, and you never get the same set twice. Every question has an instant explanation. They help you prepare for CBSE & Maharashtra HSC Board exams, JEE Main, MHT-CET, JEE Advanced and NEET UG.
Are these "Semiconductor Electronics" questions free to practise?+
Yes. Sign in with Google to practise "Semiconductor Electronics" free. Full unlimited access is ₹999/year on a launch offer until 1 December 2026. No chapter is charged separately.
How should I revise "Semiconductor Electronics" for the exam?+
Start with the Easy quiz to check your basics, then try Medium and Hard to practise applying them. There are 9 timed quizzes on this chapter, so you can come back for a fresh set instead of one you have seen. Read each explanation, retry the questions you miss, and track your accuracy until it stays high.
Are these "Semiconductor Electronics" MCQs available with answers?+
Yes. 14 sample questions are shown here in full, each with the correct option and a step-by-step "Why" explanation. Sign in free with Google to start practising, with instant scoring.
Is there negative marking in the "Semiconductor Electronics" quizzes?+
Yes. The timed quizzes use exam-style marking: +4 for a right answer, −1 for a wrong one and 0 for a skip, the same negative marking as JEE Main, JEE Advanced and NEET UG. MHT-CET and CBSE board papers have no negative marking. Our mocks for those are scored their way.
What are the important questions from Semiconductor Electronics (Class 12 Physics)?+
The questions that matter most test Energy bands in solids, Conductors, insulators, semiconductors, Band gap, Intrinsic semiconductor. This page shows 14 solved important MCQs with answers and explanations; all 90 questions on the chapter are available as timed quizzes once you sign in.
Is there an online quiz for Semiconductor Electronics?+
Yes — Class 12 Physics Semiconductor Electronics has timed online quizzes at Easy, Medium and Hard levels, with instant scoring and a worked explanation on every question. The first quiz on the chapter is free.