Gwhen a laser light of unknown wavelength is passed through two narrow slits separated by 150 μm, an interference pattern is observed on a screen 1.5 m away. the distance between the central spot and first order constructive interference is found to be 5 mm. a) find the wavelength of the laser light, in nanometers. (b) at what angle, in degrees, from the central spot is the second-order constructive interference formed?

(a) 500 nm

(b)

Solution:

Slit separation, d =

Distance from the screen, x = 1.5 m

Distance between central spot and 1st order constructive interference,

Now,

(a) To calculate the wavelength of laser light:

From Double-slit experiment, we know that the distance between the central fringe and the nth bright fringe is given by:

where

n = 1

= wavelength of the light used

Thus

(b) To calculate the angle for the formation of the constructive interference of second order:

Here

n = 2

Thus

option number c is the right answer.