Question

In a Young’s double-slit experiment, the slits are separated by 0.28 mm and the screen is placed 1.4 m away. The distance between the central bright fringe and the fourth bright fringe is measured to be 1.2 cm. Determine the wavelength of light used in the experiment.

Answer 1

Distance between the slits, d = 0.28 mm = 0.28 × 10⁻³ m
Distance between the slits and the screen, D = 1.4 m
Distance between the central fringe and the fourth (n = 4) fringe, 

u = 1.2 cm = 1.2 × 10−2 m
In case of a constructive interference, we have the relation for the distance between the two fringes as:

Hence, the wavelength of the light is 600 nm.