1. Thin Film Interference

2. Thin Film Interference

3. Condition for Constructive Interference:
The reflected rays coming out of the film (5) and the rays that reflected on the film interface with the air(2), must have a path difference of an integer multiple of l/2. This is because (2) flipped going from a less dense to a more dense medium. Note: l is the wavelength in the film.

4. Condition for Constructive Interference
Path Difference= 2t =#lfilm /2
where # =1,3, 5…
t is the thickness of the film. minimum thickness occurs when # = 1.

5. Problem
Calculate the minimum thickness of a soap bubble that results in constructive interference when a light of wavelength 500nm shines on it. Answer: 93.7 nm