Question

What will be the effect on interference fringes obtained in Young’s double slit experiment if (i) one slit is covered (ii) a source of light of higher wavelength is used. (iii) distance between two slits be increased to 1 cm and (iv) distance between screen and double slit is increased.

Answer 1

The fringe width ß is given by

ß = \(\frac{\lambda D}{d}\)

where λ is the wavelength of light incident, D is the distance between the screen and double slit and d is the distance between the two slits.

1. On covering one slit, the interference pattern will be replaced by diffraction pattern due to single slit. 
2. On increasing the wavelength of incident light λ, the fringe width will increase.
3. On increasing d by 1 cm, the fringe will disappear and there will be uniform illumination.
4. On increasing D, the fringe width will increase.