Question

In Young's double slit experiment using monochromatic light of wavelength 600 nm, 5^th bright fringe is at a distance of 0·48 mm from the centre of the pattern. If the screen is at a distance of 80 cm from the plane of the two slits, calculate:
(i) Distance between the two slits.
(ii) Fringe width, i.e. fringe separation.

Answer 1

(i)    `lambda = 600nm = 600/1000000 mm`

        `lambda =6 xx 10^-4 `mm

         D = Distance of slits from the screen = 80cm 

⇒      D = 800  mm

         `beta` = Fringe - width

      `5beta = 0.48` mm

∴       `beta = 0.48/5`

(ii)     `beta = 0.096` mm

           d = distance between 2 slits

          ` beta = (lambdaD)/d` 

   `0.48/5 = (6xx10^-4 xx 8xx10^2)/d`

⇒       `d = (6 xx8xx10^-2 xx5xx10^2)/48 = 5` mm