Show that the dispersion of a grating is D=tanθλ

Short Answer

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It is proved that the dispersion of a grating istanθλ

Step by step solution

01

Definition and concept of diffraction from a grating

An optical element with a periodic structure that divides light into a number of beams that move in diverse directions is known as a diffraction grating.

The angular distance θof the mthorder diffraction pattern produced from a grating having line separation is

dsinθ=mλ …(i)

Here, λ is the wavelength of the incident light.

02

Showing that dispersion of a grating  D=tanθλ

The dispersion is given by

D=dθdλ

Differentiate equation (i) with respect to λ to get

dcosθdθdλ=mdθdλ=mdcosθ

Substitute form of m from equation (i) to get

dθdλ=dsinθλdcosθdθdλ=tanθλ

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