Question

light of wavelength 700nm is incident on a pair of slits forming Fringe 3.0mm apart on a screen. what is the Fringe spacing when light of wavelength 350nm is used and the slit separation is double?​

Answer 1

Explanation:

For double slits: Separation of slits, a = Dλ / w

where D is the distance of the slits from the screen, λ is the wavelength and w is the fringe spacing

When λ = 600nm, w = 4.0mm

a = D (600 / 4.0)

The separation of the slits, a has now been doubled and the wavelength λ is changed to 400nm. D is still kept constant.

Fringe spacing, w = Dλ / a

The slit separation is now 2a (= 2D (600 / 4.0)).

Fringe spacing, w = D (400) / [2D (600 / 4.0)] = (400×4.0) / (2×600) = 1.3mm

Note that the units have not been converted in these equations since they would have cancelled out directly at the end of the calculations.