Question

A soap bubble appears red (λ = 633nm) at the point on its front surface nearest to the viewer. Assuming n = 1.35, what is the smallest film thickness the film could have?

Answer 1

Answer:

The smallest film thickness is 117 nm.

Explanation:

Light interference on thin films can be constructive or destructive. Constructive interference is dependent on the film thickness and the refractive index of the medium.

For the first interference (surface nearest to viewer), the minimum thickness can be expressed as:

$2t_{min} = \frac{wavelenth}{2n}$

where n is the refractive index of the bubble film.

Therefore,

$2t_{min} = \frac{633x10^{-9} }{(2)(1.35)}$

$2t_{min} =2.344x10^{-7}$

∴ $t_{min} =\frac{2.344x10^{-7} }{2}$

$t_{min} = 1.17x10^{-7} m = 117 nm.$