Question

A double slit is separation 0.5 mm is illuminated by blue light of wavelength 480nm . At what distance should a screen be placed from the double slit to obtain interference fringes that are 1.0 mm apart ? What would be the fringes - width if this distance be doubled ?

Answer 1

Explanation:

fringe width = (wavelength * distance from slits)/ distance

between slits

thus,

10^-3= 4.8*10^-7* distance / 0.5*10^-3

distance = 0.5*10^-6/4.8*10^-7

0.10*10 = 1m

since, fringe width is directly proportional to the distance, so if the distance is doubled, the fringe width will also be doubled