CUET · PHYSICS · PYQ PAPER 2025

Germanium and silicon behave as semiconductors because

A At room temperature, germanium and silicon behave as good conductors
B the energy gap between their conduction and valence bands is of the order of 1 eV
C the energy required to take out an electron from these atoms is very high
D their valence and conduction bands are overlapping

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Answer & Solution

Correct Answer

(B) the energy gap between their conduction and valence bands is of the order of 1 eV

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the energy gap between their conduction and valence bands is of the order of 1 eV This is correct. Germanium has a band gap of about 0.66 eV, and silicon has a band gap of about 1.1 eV. This gap allows semiconductors to conduct electricity under certain conditions, such as at…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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