Question

What is the relation between the dispersive power, D, of a grating and the order, n, of a spectrum?

(a) D ∝ n

(b) D ∝ N^2

(c) D ∝ 1/n

(d) D ∝ 1/N^2

I got this question in an interview for job.

The doubt is from Plane Diffraction Grating topic in division Diffraction of Engineering Physics II

Answer 1

Correct choice is (a) D ∝ n

Easiest explanation: The dispersive power of a grating is given by:

∂θ/∂λ = n/ (a + b) cosθ

Thus, as we can see D ∝ n. Hence, higher the order, higher is the dispersive power.