In an insulator, the forbidden energy gap between the valence band and conduction band is of the order of

Options

A. 1 MeV
B. 0.1 MeV
C. 1 eV
D. 5 eV

Answer

To determine the forbidden energy gap between the valence band and conduction band in an insulator, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Energy Bands**:
- In solids, electrons occupy energy levels that are grouped into bands. The two most important bands are the valence band (filled with electrons) and the conduction band (where electrons can move freely and conduct electricity).

2. **Define the Forbidden Energy Gap**:
- The forbidden energy gap (or band gap) is the energy difference between the top of the valence band and the bottom of the conduction band. In insulators, this gap is significant, preventing electrons from easily moving from the valence band to the conduction band.

3. **Identify the Characteristics of Insulators**:
- Insulators are materials that do not conduct electricity well. This is due to a large forbidden energy gap that prevents electrons in the valence band from jumping to the conduction band under normal conditions.

4. **Compare with Semiconductors**:
- For semiconductors, the forbidden energy gap typically ranges from about 0.5 eV to 1.1 eV. This smaller gap allows for some electron movement at room temperature, enabling conductivity.

5. **Determine the Range for Insulators**:
- For insulators, the forbidden energy gap is significantly larger than that of semiconductors. It generally ranges from about 3 eV to 6 eV.

6. **Evaluate the Given Options**:
- The options provided are:
- 1 mega electron volt (MeV)
- 0.1 mega electron volt (MeV)
- 1 electron volt (eV)
- 5 electron volts (eV)
- Since 1 MeV = 1,000,000 eV, both 1 MeV and 0.1 MeV are far too large for the context of insulators. The value of 1 eV is too small, as it falls within the range of semiconductors.

7. **Select the Correct Answer**:
- The only viable option left is 5 electron volts (eV), which falls within the typical range for the forbidden energy gap in insulators.

### Final Answer:
The forbidden energy gap between the valence band and conduction band in an insulator is of the order of **5 electron volts (eV)**.

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