Interference 

To get complimentary pattern of initial interference pattern , path length Δp between the reflected rays of

respective incident rays should be (2n+1)( λ/2 )

 

where n is an integer , n = 1, 2, 3.... etc and λ is wavelength

 

Δp = ( 2n + 1 ) ( λ/2 ) = [ n + (1/2) ] λ  ....................(1)

 

Path difference due to reflection at intermediate layer = μ × 2d ................(2)

 

where μ is refractive index of liquid and d is the thickness of liquid film

 

Since refractive index varies with respect to time , from eqn.(1) and (2)

 

( μ(0) - 0.1 t ) × 2d = [ n + (1/2) ] λ

 

( 1.4 - 0.1 t ) × 2d = [ n + (1/2) ] λ

 

By knowing liquid film thickness d and wavelength of light used ,

we get time t that will produce complimentary interference pattern