Find the minimum thickness of a soap bubble that appears red when illuminated by white light...

Question:

Find the minimum thickness of a soap bubble that appears red when illuminated by white light perpendicular to its surface. Take the wavelength to be 680 nm, and assume the same index of refraction as water.

Constructive Interference

Interference happens when a pair of light pass through each other. Superposition, the adding of waves together, is observable. Constructive interference happens when the maxima of two waves add up together wherein the waves are both in phase. This results in the amplitude of the wave to be the sum of the individual amplitudes. Additionally, the minima of the said waves will not be aligned.

{eq}2t = \frac {\lambda_n}{2} = \frac {\lambda}{2n} \\ t = \frac {\lambda}{4n} = \frac {6.80 \times 10 ^\text{-7} m}{4 (1.33)} = 1.278 \times 10^\text{-7} = 128 nm {/eq}