Question

For an insulator, the forbidden energy gap is:

• A. Zero
• B. \(1 { eV}\)
• C. \(2 { eV}\)
• D. \(5 { eV}\)

Hint:

- Conductors: No band gap (\(E_g = 0\)). - Semiconductors: Small band gap (\(1 - 2\) eV). - Insulators: Large band gap (\(> 3\) eV, typically \(5\) eV).

Answer 1

The Correct Option is D

Step 1: Understanding the Forbidden Energy Gap The forbidden energy gap (also known as the band gap) is the energy difference between the valence band and the conduction band in a solid material. It determines the electrical conductivity of a material. 
Step 2: Classification of Materials Based on Band Gap - Conductors (\(E_g = 0\) eV): No band gap; electrons move freely. - Semiconductors (\(E_g \approx 1 - 2\) eV): Small band gap; thermal energy can excite electrons. - Insulators (\(E_g>3\) eV, typically around 5 eV): Large band gap; electrons cannot easily transition to the conduction band. 
Step 3: Correct Option For an insulator, the band gap is typically greater than 3 eV, and in most cases, it is around 5 eV. Hence, the correct option is: \[ E_g = 5 { eV} \]