Class 12 Physics NCERT Solutions

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Semiconductor Electronics Class 12 Physics NCERT Solutions

The complete NCERT exercise solutions for Chapter 14, Semiconductor Electronics — 6 questions from 14.1 to 14.6, each worked through step by step in the CBSE marking pattern. Energy bands, intrinsic and extrinsic semiconductors, the p-n junction diode, rectifiers, special-purpose diodes and the transistor.

Class:12Subject:PhysicsChapter:14

4 Key Formulas25 Practice MCQs

DWritten byDeep Narayan

UpdatedSeptember 2026

Key Concept Summary

How many questions are in NCERT Class 12 Physics Chapter 14?

Chapter 14 carries 6 exercise questions, numbered 14.1 to 14.6. All of them are solved step by step on this page, along with the chapter's key formulas and exam pointers.

Table of Contents7 sections

Revision & Practice

Chapter Overview

Semiconductor physics runs on a small set of ideas: intrinsic conduction and how doping with pentavalent or trivalent atoms creates n-type and p-type material, the energy-band picture with its forbidden gap, and the p-n junction whose barrier is lowered by forward bias and raised by reverse bias. Rectification is the junction at work — half-wave and full-wave. Every question below is from the NCERT Class 12 textbook (rationalised edition), answered in the board pattern.

Board pattern

n-type: pentavalent dopants donate electrons (electrons majority, holes minority). p-type: trivalent dopants accept electrons (holes majority). Band gaps run Eg(C) > Eg(Si) > Eg(Ge). In an unbiased junction, carriers diffuse down their concentration gradient. Forward bias lowers the potential barrier; reverse bias raises it. Each input cycle gives one output pulse in half-wave rectification but two in full-wave.

$Ex 14.1 — True statement about n-type silicon$
$Ex 14.2 — True statement about p-type semiconductors$
$Ex 14.3 — Band gaps of carbon, silicon and germanium$
$Ex 14.4 — Why holes diffuse across an unbiased p-n junction$
$Ex 14.5 — Effect of forward bias on the potential barrier$
$Ex 14.6 — Output frequency of half-wave and full-wave rectifiers$

NCERT Exercise 14.1 — True Statement About n-Type Silicon

1Exercise question

Step-by-step solution

1n-type silicon is doped with pentavalent atoms (e.g. phosphorus), each donating one free electron.
2The dopant atoms supply electrons, making electrons the majority carriers and holes the minority carriers.
3That matches statement (c).

Final answer

NCERT Exercise 14.2 — True Statement About p-Type Semiconductors

1Exercise question

Step-by-step solution

1p-type material is doped with trivalent atoms (e.g. boron), creating an excess of holes.
2Holes become the majority carriers and electrons the minority carriers.
3That is statement (d): Holes are majority carriers and trivalent atoms are the dopants.

Final answer

(d) Holes are majority carriers and trivalent atoms are the dopants.

NCERT Exercise 14.3 — Band Gaps of Carbon, Silicon and Germanium

1Exercise question

Step-by-step solution

1Band gap widens as the atomic size shrinks and covalent binding strengthens, in the order Ge → Si → C.
2So Eg(C) is the largest and Eg(Ge) the smallest.
3That matches statement (c).

Final answer

NCERT Exercise 14.4 — Holes Diffuse Across an Unbiased Junction

1Exercise question

Step-by-step solution

1Diffusion is driven by the concentration gradient, not by attraction or by a built-in potential difference acting on holes alone.
2Hole concentration is much higher on the p-side, so holes naturally diffuse toward the n-side.
3That matches statement (c).

Final answer

NCERT Exercise 14.5 — Forward Bias and the Potential Barrier

1Exercise question

Step-by-step solution

1Forward bias applies an external voltage opposite to the junction field.
2This pushes the diffusion of majority carriers forward and reduces the width and height of the depletion barrier.
3That matches statement (c): it lowers the potential barrier.

Final answer

NCERT Exercise 14.6 — Output Frequency of Rectifiers

1Exercise question

Step-by-step solution

1A half-wave rectifier passes only one half of each input cycle, so the number of output pulses equals the input frequency.
2Output frequency (half-wave) = 50 Hz.
3A full-wave rectifier inverts and passes both halves, giving two output pulses per input cycle.
4Output frequency (full-wave) = 2 × 50 = 100 Hz.

Final answer

Half-wave: 50 Hz. Full-wave: 100 Hz.

Quick Revision

Key formulas at a glance

Memorise these equations — direct application numericals and derivations in CBSE & JEE frequently hinge on these.

Diode current (forward)

I = I_{0} (e^{\frac{V}{η V _{T}}} - 1)

Rectified current (half-wave)

I_{d c} = \frac{I _{0}}{π}

Transistor current relation

I_{C} = β I_{B}, I_{E} = I_{C} + I_{B}

Energy gap

E_{g} = E_{C} - E_{V}

Exam Strategy

How this chapter is asked

High-yield question patterns observed across CBSE boards, JEE Main & Advanced, and NEET.

A diode conducts in the forward direction because the barrier potential is reduced, and in reverse it blocks until Zener or avalanche breakdown — the reverse V-I characteristic is the one to read carefully.
A p-type semiconductor has more holes than electrons and an n-type the reverse, so the majority carriers change across the junction; the depletion region contains no mobile charge.

FAQ

Frequently asked questions

How many questions are in NCERT Class 12 Physics Chapter 14 (Semiconductor Electronics)?

There are 6 exercise questions in this chapter, numbered 14.1 to 14.6. Every one is solved step by step on this page in the official NCERT numbering.

Which formulas come up in Semiconductor Electronics Class 12 Physics?

The formulas this chapter's questions actually turn on are: Diode current (forward), Rectified current (half-wave), Transistor current relation, Energy gap. They are listed with their expressions in the key formulas section below, and the solved questions show where each one is used.

Is Semiconductor Electronics important for JEE Main and NEET?

Important — the diode characteristic, half-wave and full-wave rectification and the transistor relations are formula-based and reliably asked in JEE Main, NEET and the boards.

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