Assertion: Standard optical diffraction cannot be used for discrimination between different X-ray wavelengths.
Reason: The grating spacing is not of the order of X-ray wavelengths.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true statement but resaon is false.
D. If both assertion and reason are false.

Answer

a

Explanation

`X`-rays are electromagnetic radiations whose wavelength are of the order of `1 Å(=10^(-10)m)`. A standard optical diffraction grating cannot be used to discriminate between different wavelengths in the `X`-rays wavelength range. For `i=1Å (= 0.1 nm)` and `d= 3000nm`, for example, the first order maximum occurs at,
`theta= sin^(-1)((m lambda)/(d))= sin^(-1).((1) (0.1))/(3000)= 0.0019^(@)`
This is to close to the central maximum to be practical. A grating with `d= lambda` is desirable, but since, `X`-rays wavelengths are about equal to atomic diameter, such gratings cannot be constructed directly. Hence, option(a) is correct.