Which of the following is incorrect statement about the Bragg's equation `n lambda = 2d sin theta` ?

Options

A. n, represents order of reflection
B. `lambda`, represents wavelength of UV - rays used
C. `theta`, represents angle of incidence
D. d, represents distance between two parallel planes

Answer

To determine which statement about Bragg's equation \( n \lambda = 2d \sin \theta \) is incorrect, let's analyze each part of the equation and the statements provided:

### Step-by-Step Solution:

1. **Understanding Bragg's Law**:
Bragg's law states that when X-rays are incident on a crystal surface, constructive interference occurs when the path difference between rays reflected from successive atomic layers equals a whole number of wavelengths.

2. **Identifying Variables in Bragg's Equation**:
- \( n \): This represents the order of reflection, which is a whole number (1, 2, 3, ...).
- \( \lambda \): This is the wavelength of the incident rays.
- \( d \): This is the distance between two parallel planes of atoms in the crystal.
- \( \theta \): This is the angle of incidence (and also the angle of reflection).

3. **Evaluating the Statements**:
- **Statement 1**: "n represents order of reflection."
- This is **correct**.
- **Statement 2**: "lambda represents wavelength of UV rays used."
- This is **incorrect**. In Bragg's law, the wavelength \( \lambda \) refers to X-rays, not UV rays.
- **Statement 3**: "theta represents angle of incidence."
- This is **correct**.
- **Statement 4**: "d represents the distance between two parallel planes."
- This is **correct**.

4. **Conclusion**:
The only incorrect statement is the second one, which states that \( \lambda \) represents the wavelength of UV rays used. In reality, X-rays are used in Bragg's law.

### Final Answer:
The incorrect statement about Bragg's equation \( n \lambda = 2d \sin \theta \) is that "lambda represents wavelength of UV rays used."