Case: Read the passage and answer the question.
The band gaps of two materials are given below.
Diamond: 5.4 eV
GaAs: 1.43 eV
Based on this, what can you infer?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → It is easier for an electron to conduct electricity in GaAs.
The smaller the energy gap between the valence band and the conduction band, the more easily electrons gain enough energy to cross it and conduct. From the passage, GaAs has a gap of 1.43 eV while diamond has a gap of 5.4 eV.
Option (1) It is easier for an electron to conduct electricity in diamond. — Incorrect. The gap of diamond, 5.4 eV, is more than 3 eV. So thermal energy cannot lift its electrons into the conduction band, and diamond behaves as an insulator.
Option (2) It is easier for an electron to conduct electricity in GaAs. — Correct. GaAs has a small gap of 1.43 eV, less than 3 eV. So at room temperature some electrons from the valence band cross the gap into the conduction band. They can move there and carry current.
Option (3) The conduction in these two materials depends solely on temperature. — Incorrect. At the same temperature, GaAs conducts while diamond does not. So the energy gap of each material decides the conduction. Temperature alone does not decide it.
NCERT (2026-27):
Classification of Metals, Conductors and Semiconductors – “Case III: … Here a finite but small band gap (Eg < 3 eV) exists. Because of the small band gap, at room temperature some electrons from valence band can acquire enough energy to cross the energy gap and enter the conduction band. These electrons (though small in numbers) can move in the conduction band.”