Length cannot be measured by

Options

A. Fermi
B. Debye
C. Micron
D. Light year

Answer

To determine which unit cannot be used to measure length, we will analyze each option provided.

### Step-by-Step Solution:

1. **Identify the Units Provided**: The options given are Fermi, Debye, Micron, and Light year.

2. **Analyze Each Unit**:
- **Fermi**: This is a unit of length used to measure very small distances, particularly at the atomic level. It is equivalent to \(10^{-15}\) meters. Thus, Fermi can measure length.
- **Debye**: This is a unit of electric dipole moment, not a unit of length. It is used in the context of molecular physics and chemistry to describe the polarity of molecules. Therefore, Debye cannot measure length.
- **Micron**: Also known as a micrometer, this unit is equal to \(10^{-6}\) meters and is commonly used to measure small distances. Hence, Micron can measure length.
- **Light year**: This unit measures the distance that light travels in one year, which is approximately \(9.46 \times 10^{12}\) kilometers. Thus, a Light year can measure length.

3. **Conclusion**: Among the options, Debye is the only unit that does not measure length. Therefore, the answer is **Option B (Debye)**.