Free practice › Class 12 › Physics › Chapter 14
Semiconductor Electronics: Materials, Devices and Simple Circuits — NEET & JEE MCQs with answers
This chapter introduces solid-state semiconductor electronics, covering the energy-band classification of conductors, semiconductors, and insulators; the properties and carrier physics of intrinsic and extrinsic (doped) semiconductors; the p-n junction and its behaviour under forward and reverse bias; and applications of the junction diode as a rectifier.
Topics in this chapter
- 14.1 Introduction
- 14.2 Classification of Metals, Conductors and Semiconductors
- 14.3 Intrinsic Semiconductor
- 14.4 Extrinsic Semiconductor
- 14.5 p-n Junction
- 14.6 Semiconductor Diode
- 14.7 Application of Junction Diode as a Rectifier
Free practice questions
The output of a half-wave rectifier has a ripple frequency of 400 Hz. If the same ac source now feeds a full-wave rectifier, the output ripple frequency will be:
- A. $200\,\text{Hz}$
- B. $800\,\text{Hz}$
- C. $400\,\text{Hz}$
- D. $1600\,\text{Hz}$
Show answer
Answer: B — Half-wave output frequency = input, so input = 400 Hz. Full-wave ripple = 2 x input = 800 Hz.
NCERT Class 12 Physics Ch 14 ("What is the output frequency of a full-wave rectifier")
During diffusion at the junction, holes and electrons move in which directions?
- A. holes p → n and electrons n → p
- B. both holes and electrons p → n
- C. both holes and electrons n → p
- D. holes n → p and electrons p → n
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Answer: A — Holes diffuse from p-side to n-side and electrons diffuse from n-side to p-side, driven by the concentration gradient.
NCERT Class 12 Physics Ch 14 ("concentration gradient across p-, and n- sides")
A diode in forward bias shows a change of $\Delta V=0.2\,\text{V}$ for a change of $\Delta I=8\,\text{mA}$. Its dynamic resistance is:
- A. $250\,\Omega$
- B. $2.5\,\Omega$
- C. $25\,\Omega$
- D. $0.025\,\Omega$
Show answer
Answer: C — $r_d=\dfrac{\Delta V}{\Delta I}=\dfrac{0.2\,\text{V}}{8\,\text{mA}}=25\,\Omega$ (convert mA to A: 8\,mA $=0.008\,$A).
NCERT Class 12 Physics Ch 14 ("dynamic resistance")
The free electron moving independently under an applied field gives rise to:
- A. Displacement current
- B. Hole current $I_h$
- C. Zero current
- D. Electron current $I_e$
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Answer: D — The free electron moves completely independently as a conduction electron and gives rise to an electron current, Ie.
NCERT Class 12 Physics Ch 14 ("electron current, Ie")
For germanium, the outermost orbit is the:
- A. fifth orbit (n = 5)
- B. third orbit (n = 3)
- C. second orbit (n = 2)
- D. fourth orbit (n = 4)
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Answer: D — For Ge the outermost orbit is the fourth orbit (n = 4).
NCERT Class 12 Physics Ch 14 ("is the fourth orbit")
The seed of the development of modern solid-state semiconductor electronics goes back to:
- A. The 1948
- B. The 1950's
- C. The 1920's
- D. The 1930's
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Answer: D — The text states the seed of the development of modern solid-state semiconductor electronics goes back to the 1930's.
NCERT Class 12 Physics Ch 14 ("goes back to 1930's")
For a semiconductor in thermal equilibrium $n_i = 1.5 \times 10^{16}$ m$^{-3}$ and the hole concentration is $n_h = 2.25 \times 10^{10}$ m$^{-3}$. Using $n_e n_h = n_i^2$, the electron concentration $n_e$ is:
- A. $1 \times 10^{22}$ m$^{-3}$
- B. $1 \times 10^{21}$ m$^{-3}$
- C. $2.25 \times 10^{10}$ m$^{-3}$
- D. $1 \times 10^{23}$ m$^{-3}$
Show answer
Answer: A — $n_e = n_i^2/n_h = (1.5 \times 10^{16})^2/(2.25 \times 10^{10}) = 1 \times 10^{22}$ m$^{-3}$.
NCERT Class 12 Physics Ch 14 ("nenh = ni")
The lattice spacing a of Germanium is:
- A. 6.10 Å
- B. 5.43 Å
- C. 3.56 Å
- D. 5.66 Å
Show answer
Answer: D — Lattice spacings for C, Si, Ge are 3.56, 5.43 and 5.66 Angstrom; Germanium is 5.66 Angstrom.
NCERT Class 12 Physics Ch 14 ("3.56, 5.43 and 5.66")
In a half-wave rectifier, a pulsating voltage appears across the load:
- A. During both half cycles equally
- B. Continuously with a steady value
- C. Only when the diode is reverse biased
- D. Only during the half cycles when the diode is forward biased
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Answer: D — A pulsating voltage appears across the load only during the half cycles of the ac input during which the diode is forward biased.
NCERT Class 12 Physics Ch 14 ("a pulsating voltage will appear across the load only during the half cycles")
The resistivity of semiconductors lies approximately in the range:
- A. $10^{11}$–$10^{19}$ Ω m
- B. $10^{-2}$–$10^{-8}$ Ω m
- C. $10^{2}$–$10^{8}$ Ω m
- D. $10^{-5}$–$10^{6}$ Ω m
Show answer
Answer: D — Semiconductor resistivity is intermediate, ρ ~ $10^{-5}$–$10^{6}$ Ω m.
NCERT Class 12 Physics Ch 14 ("resistivity or conductivity intermediate")
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