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Physics · 2025 · 3 marks
Semiconductor Electronics: Materials, Devices and Simple CircuitsClassification of Metals, Conductors and Semiconductors3 marksUnderstandshort answer
CBSE 2025 · Region 5 · Set 1 · Q22
(a) Draw the energy-band diagrams for conductors, semiconductors and insulators at T =0 K. How is an electron-hole pair formed in a semiconductor at…
(a)
Draw the energy-band diagrams for conductors, semiconductors and insulators at $\displaystyle \mathrm{T}=0 \mathrm{~K}$. How is an electron-hole pair formed in a semiconductor at room temperature?
(b)
Carbon and silicon both, are members of IV group of periodic table and have the same lattice structure. Carbon is an insulator whereas silicon is a semiconductor. Explain.
Marking-scheme solution
(a)
At room temperature, thermal energy is sufficient for electrons to make them free from the bonds and create a vacancy called a hole. Hence an electron-hole pair is formed.
(b)
The valence electrons in carbon and silicon lie in the second and third orbit respectively. So the energy required to take out an electron will be less for silicon as compared to carbon. Hence the number of free electrons for conduction in silicon is significant but negligibly small for carbon.
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CBSE Class 12 Physics past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.