Question

Explain how you would find the specific wavelength of a light source using a diffraction grating?

Answer 1

Explanation:

Using diffraction grating

Considering the expression:

$d\times sin\theta=m\times \lambda$

Where, m = 1, 2, .....

d is the distance between the slits.

The formula can be written as:

$sin\theta=\frac {\lambda}{d}\times m$ ....1

The location of the bright fringe is determined by :

$y=L\times tan\theta$

Where, L is the distance between the slit and the screen.

For small angle , $sin\theta=tan\theta$

So,  

Formula becomes:

$y=L\times sin\theta$

Using 1, we get:

$y=L\times \frac {\lambda}{d}\times m$

By finding the distance between the first fringe (m = 1) fringe and the central maximum (y) , wavelength can be calculated as the distance between slit and scree (L) and the distance between the slits (d) are known in an experiment.