Step-by-step explanation:
Using diffraction grating
Considering the expression:
Where, m = 1, 2, .....
d is the distance between the slits.
The formula can be written as:
....1
The location of the bright fringe is determined by :
Where, L is the distance between the slit and the screen.
For small angle ,
So,
Formula becomes:
Using 1, we get:

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.