# Soap bubble

1. May 2, 2016

### rgold

1. The problem statement, all variables and given/known da
A soap bubble 500 nm thick is illuminated with white light. The index of refraction of

this unique soap film is 1.35 for all colors (no dispersion). a) What wavelengths are not

reflected?

2. Relevant equations

2nt=mL
2nt=m(L/2)
3. The attempt at a solution
for m=1 2(1.35)(500nm)=1350nm
for m=2 =675nm
am i doing this right? i do not really understand what the question is looking for.

2. May 2, 2016

### Simon Bridge

... then you are probably not doing it right.
Even if you got the right answer, it would only be by accident.

Why would some wavelengths not get reflected off the soap bubble?

3. May 3, 2016

### rgold

If they get absorbed they would not be reflected right? But I don't know how to translate this

4. May 3, 2016

### Simon Bridge

Not quite: the light does not have to be absorbed.
You have probably just done a section on thin films. Recall that it depends on interference: the reflected ray off the bottom (inner) surface of the bubble interferes with the reflected ray off the top (outer) surface. Also recall that reflection may involve a phase change.

If you missed it in class here's a crash course:
http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/thinfilm.html

You can find other examples online under "thin film physics".