Question

The interference pattern, using two coherent sources of light; the fringe width is____? a)directly proportional to wavelength.
b) inversely proportional to square of wavelength
3)inversely proportional to wavelength.
4)directly proportional to square of the wavelengh

Answer 1

Answer :(a) fringe width is directly proportional to wavelength .

Explanation :- as you know , fringe width is the separation between two consecutive bright or consecutive dark .
We know, for bright , yn = nλD/d ,
And for dark , yn = (2n-1)λD/d
Here, λ is wavelength of wave , d is the separation between slits and D is the separation between slit and screen.

Now, fringe width = Y₂ - Y₁ = 2λD/d - λD/d = λD/d [ when we take bright ]
also fringe width is same for dark = 3λD/2d - λD/2d = λD/d

Finally, fringe width = λD/d , hence, fringe width is directly proportional to wavelength.