Read the following passage and answer the questions.
A student studies a slab of pure silicon. It contains about \(5\times10^{28}\) atoms per cubic metre. The atoms are arranged in a diamond-like structure, and each silicon atom has four valence electrons. Germanium has the same kind of structure. First, the slab is kept in a cold chamber at a temperature very close to 0 K. It is then taken out and allowed to warm up to room temperature (300 K). At this temperature, the intrinsic carrier concentration of silicon is about \(1.5\times10^{16}\ \mathrm{m^{-3}}\). Finally, the student connects a battery and an ammeter in series with the slab. The ammeter shows a small but steady current. The slab is kept at room temperature throughout this test.
In the warmed slab, a few electrons break away from their bonds. Each of them leaves a vacancy in its bond. If \(q\) is the magnitude of the electronic charge, the effective charge of this vacancy is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \(+q\)
The electron that breaks away carries a charge \( -q \). The bond it leaves is now short of this negative charge, so the vacancy acts as a charge \( +q \). This vacancy is called a hole. It behaves like a free particle with a positive charge.
NCERT (2026-27):
Intrinsic Semiconductor – “… The neighbourhood, from which the free electron (with charge –q) has come out leaves a vacancy with an effective charge (+q). This vacancy with the effective positive electronic charge is called a hole.”