a) Why are coherent sources necessary to produce a sustained interference pattern?
(b) In Young’s double slit experiment using monochromatic light of wavelength 
, the intensity of light at a point on the screen where path difference is 
is K units. Find out the intensity of light at a point where path difference is 
.
a)
Coherent sources have almost the same wavelength. Coherent sources are necessary to ensure that the positions of maxima and minima do not change with time. Thereby, producing a sustained interference pattern.
b)
Wavelength of monochromatic light = 
Path difference = 
So, phase difference, 
Intensity of light = K units
Intensity is given by, I 
When path difference is 
, phase difference becomes 
Intensity of light I’ = 
, is the new intensity of light.
