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, we first need to understand the components of the equation:

1. **Bragg's Equation**: The equation \( n \lambda = 2d \sin \theta \) is used to describe the condition for constructive interference of X-rays scattered by a crystal lattice.

2. **Components of the Equation**:
- \( n \): This represents the order of reflection, which is an integer (0, 1, 2, ...).
- \( \lambda \): This is the wavelength of the X-rays used in the experiment.
- \( d \): This is the distance between the parallel planes of atoms in the crystal lattice.
- \( \theta \): This is the angle of incidence (or the angle at which the X-rays hit the crystal planes).

Now, let’s analyze the statements regarding the Bragg's equation:

### Step-by-Step Analysis:

1. **Order of Reflection**: The statement that \( n \) represents the order of reflection is correct. This is a fundamental aspect of Bragg's law.

2. **Wavelength**: The statement that \( \lambda \) is the wavelength of UV rays is incorrect. In the context of Bragg's equation, \( \lambda \) specifically refers to the wavelength of X-rays, not UV rays.

3. **Distance Between Planes**: The statement that \( d \) is the distance between two parallel planes is correct. This is a key parameter in determining the diffraction pattern.

4. **Angle of Incidence**: The statement that \( \theta \) represents the angle of incidence is also correct. This angle is crucial for calculating the path difference leading to constructive interference.

### Conclusion:
The incorrect statement about Bragg's equation is that \( \lambda \) is the wavelength of UV rays. Instead, it should be stated that \( \lambda \) is the wavelength of X-rays.

### Final Answer:
The incorrect statement is: "Lambda is the wavelength of UV rays."

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