Question

Which of the following equation is used for the constructive interference in optical grating?

(a) a tanα=nλ

(b) a cotα=nλ

(c) a sinα=nλ

(d) a secα=nλ

This question was posed to me by my college director while I was bunking the class.

My enquiry is from Diffraction topic in division X-Ray Diffraction of Solid State Chemistry

Answer 1

Right option is (c) a sinα=nλ

To explain I would say: This equation gives the conditions under which constructive interference occurs and relates the spacing of the grating to the light wavelength and the diffraction order, n. Hence, depending on the value of a sinα, one or more diffraction orders, corresponding to n=1,2, etc, may be observed.