Question

White light is incident on a soap film (n = 1.33, thickness = 937.0 nm ) suspended in air.

If the incident light makes a 45 ? angle with the normal to the film, what visible wavelength(s) will be constructively reflected?

Answer 1

for constructive reflection,

2 n d cos (theta) = (m-1/2) lamda

2( 1.33) ( 937 x 10^-9) cos 45 = ( 1/2) lamda ( for m = 1)

3524 nm = lamda----not fall in visible range

2( 1.33) ( 937 x 10^-9) cos 45 = ( 2-1/2) lamda ( for m= 2)

1174.9 nm --------------not fall in visible range

2( 1.33) ( 937 x 10^-9) cos 45 = ( 3-1/2) lamda ( for m= 3)

704 . 962 nm ------falls in visiblee light

2( 1.33) ( 937 x 10^-9) cos 45 = ( 4-1/2) lamda ( for m= 4)

503.54 nm ------------------falls in visible light