Question

What is the minimum thickness of a thin film `(mu=1.2)` that results in constructive interference in the reflected light? If the film is illuminated with light whose wavelength in free space is `lambda=500nm` ?
A. 104 nm
B. 200 nm
C. 300 nm
D. 400 nm

Answer 1

Correct Answer - A
For constructive interference in case of soap film
`2mut=(n-1/2)lambda (n-1,2,3,....)`
For minima thickness `t, n=1 or 2mut=lambda//2`
The minima thickness of a soap bubble
`t=lambda/(4mu)=500/(4xx12)=104.17 approx104nm`