Semiconductor Electronics — Class 12 Physics NCERT Solutions (Free)

Free step-by-step NCERT solutions for Class 12 Physics chapter "Semiconductor Electronics" — 5 important questions with detailed answers for CBSE board exam preparation.

✓ 100% Free ✓ No Login Needed ✓ NCERT / CBSE Aligned ✓ Download as PDF

TL;DR: Free step-by-step NCERT solutions for Class 12 Physics chapter "Semiconductor Electronics" — 5 important questions with detailed answers for CBSE boar…

Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated Jul 23, 2026

🤖 Stuck on any question? Ask Syllab's free AI Tutor for a step-by-step explanation — instant, unlimited, no login.

Key Questions Covered:

Explain the band theory of solids. Distinguish between conductors, insulators…
Explain the p-n junction and how it rectifies current (diode action).
Explain the transistor (BJT). Describe the three operating regions and derive…
An npn transistor has β = 100. If base current is 20 μA, find collector and e…
What is feedback in amplifiers? Explain negative feedback and its effects on …

Solutions Summary:

Question	Status
Explain the band theory of solids. Distinguish between co…	✓ Solved
Explain the p-n junction and how it rectifies current (di…	✓ Solved
Explain the transistor (BJT). Describe the three operatin…	✓ Solved
An npn transistor has β = 100. If base current is 20 μA, …	✓ Solved
What is feedback in amplifiers? Explain negative feedback…	✓ Solved

Showing 5 of 5 questions

Q1: Explain the band theory of solids. Distinguish between conductors, insulators, and semiconductors.

Band Theory of Solids: In isolated atoms, electrons occupy discrete energy levels. In solids, atoms are closely packed, and these levels split into bands of closely-spaced levels. Formation of Bands: 1. When N atoms combine, each level splits into N levels 2. Levels so close they form continuous band 3. Band width depends on atomic spacing 4. Bands separated by energy gaps (forbidden zones) Key Bands: Valence Band: Outermost electrons, partially filled Conduction Band: Higher energy band, elec...

Q2: Explain the p-n junction and how it rectifies current (diode action).

p-n Junction: Contact between p-type and n-type semiconductor materials. Formation of p-n Junction: 1. p-type: doped with acceptors (holes are majority carriers) 2. n-type: doped with donors (electrons are majority carriers) 3. At junction: electrons diffuse from n to p, holes diffuse from p to n 4. Diffusion leaves positive ions in n-type, negative ions in p-type 5. Creates electric field opposing further diffusion 6. Equilibrium reached (built-in potential V₀ ≈ 0.7 V for Si) Depletion Region...

Q3: Explain the transistor (BJT). Describe the three operating regions and derive the current gain relationship.

Bipolar Junction Transistor (BJT): Three-terminal device with two back-to-back p-n junctions for current and voltage amplification. Structure: - Emitter (E): heavily doped, source of charge carriers - Base (B): lightly doped, controls carrier injection - Collector (C): lightly doped, collects carriers - Two types: npn and pnp Basic Operating Principle: 1. Small base current controls large collector current 2. Base-emitter junction: forward biased (conducts) 3. Base-collector junction: reverse ...

Q4: An npn transistor has β = 100. If base current is 20 μA, find collector and emitter currents in active region.

Given: Current gain: β = 100 Base current: I_B = 20 μA = 20 × 10⁻⁶ A Transistor in active region Collector Current: In active region: I_C = β × I_B I_C = 100 × 20 × 10⁻⁶ I_C = 2000 × 10⁻⁶ A = 2 mA = 0.002 A Emitter Current: From current continuity: I_E = I_B + I_C I_E = 20 × 10⁻⁶ + 2000 × 10⁻⁶ I_E = 2020 × 10⁻⁶ A = 2.02 mA = 0.00202 A Alpha (current transfer ratio): α = I_C/I_E = 2000/2020 = 0.9901 ≈ 0.99 Verification: β = α/(1 - α) = 0.99/0.01 = 99 ≈ 100 ✓ Percentage Distribution: - Base c...

Q5: What is feedback in amplifiers? Explain negative feedback and its effects on gain and stability.

Feedback: Returning a portion of output signal to input, modifying overall behavior. Types of Feedback: 1. Negative Feedback: Output opposes input (reduces gain but improves stability) 2. Positive Feedback: Output aids input (increases gain, can cause oscillation) Negative Feedback System: Input → [Gain Block] → Output ↑ [Feedback Network] Feedback Factor β_f = V_f/V_o (fraction fed back) Loop Gain: L = A × β_f (open-loop gain × feedback factor) Closed-loop gain: A_f = A/(1...

Showing 5 of 5 questions. Visit the full page for complete solutions.