An arrangement for demonstrating interference using light is shown.
The wavelength of the light from the laser is 
. The light is incident normally on the double slit. The separation of the two slits is 
. The perpendicular distance between the double slit and the screen is 
.
Coherent light waves from the slits form an interference pattern of bright and dark fringes on the screen. The distance between the centres of two adjacent bright fringes is 
. The central bright fringe is formed at point P.
Explain why a bright fringe is produced by the waves meeting at point P.
Calculate distance
.
