Question

Indicate which one of the following statements is NOT CORRECT?

• A. Intensities of reflections from different crystallographic planes are equal
• B. According to Bragg's law higher order reflections have high \( h \) values for a given wavelength of radiation
• C. For a given wavelength of radiation there is a smallest distance between the crystallographic planes which can be determined
• D. Bragg's law may predict a reflection from a crystallographic plane to be present but it may be absent due to the crystal symmetry

Hint:

Bragg's law deals with diffraction, but the intensity of the reflection depends on the crystal structure and symmetry.

Answer 1

The Correct Option is A

Step 1: Understanding Bragg's Law.
Bragg's law explains the condition for constructive interference of X-rays diffracted by a crystal lattice: \[ n\lambda = 2d \sin \theta \] where \( \lambda \) is the wavelength, \( d \) is the interplanar distance, and \( \theta \) is the angle of diffraction.
Step 2: Analysis of the options.
- (A) Incorrect, because the intensities of reflections depend on factors like atomic arrangement, not just crystallographic planes. - (B) Correct statement, higher order reflections have higher \( h \)-values for a given wavelength. - (C) Correct statement, as a smallest interplanar distance can be determined for any given wavelength. - (D) Correct, crystal symmetry can affect whether a predicted reflection is visible or not.
Step 3: Conclusion.
The incorrect statement is (A). Hence, the correct answer is option (A).

Final Answer: \[ \boxed{\text{(A) Intensities of reflections from different crystallographic planes are equal.}} \]