Question

2. Consider a soap film (n = 140) that is hanging in a soap bubble wand. Air is on either side of the soap film. The thickness of the film near the top of the wand is very small (e.g. <<400 nm) and increases monotonically in the downward direction. Suppose that white light is normally incident upon the soap film, and that we look at the light reflected by the film: a. Show why the film looks black near the top of the wand b. The rest of the film shows colors. What is the smallest film thickness that causes 550 nm light to be absent from the reflected light pattern.
PLEASE DO ALL PARTS!!

Answer 1

Part (a) An we know for the Reflection Interference through films if smaller than 400 nm width all the right passes through film d(thickness) doublelessthan 400 nm All variable light crenes film at Top no ene can be Reflected. Part(b) for 550 nm absent by Reflection (Interference) Restructive interference in film when 2 nd = mn form = 1 thichem d = 1. 964 times 10^-7 m d = lambda/2n) = 550nm/ 2 times 1. 4