# Waves Light and Sound

1. Feb 2, 2009

### stickplot

Ok so ive been thinking this problem over and over and I understand the problem and its concept but I dont know where to start someone please guide me through this

i know it will be destructive interference at 180 but I dont know what else to apply to the problem someone help please.

Light waves of which wavelength will destructively interfere due to the thickness of the bubble film? The bubble film thickness is 165 nm, with an index of refraction of n = 1.3.

It also contains a picture just showing the different light waves

a= 430 nm
b= 650 nm
c= 860 nm
d= 285 nm

2. Feb 2, 2009

### Delphi51

So, part of the wave is reflected from the front surface and part from the back surface of the bubble and these two reflections interfere destructively?

If so, in order for the interference to be destructive the wave passing through the bubble thickness twice must be delayed by half a wavelength. Thus the thickness of the bubble is a quarter of a wavelength.

There is another wrinkle. The wavelength of the light decreases when it passes into the bubble material, by a factor of n. The thickness is a quarter of this reduced wavelength, but your answer should be expressed as its regular wavelength in air.

3. Feb 2, 2009

### stickplot

o ok. i now understand the concept well now, but how would i put that in a formula to see which one is destructing?

4. Feb 2, 2009

### Delphi51

thickness = 1/4*wavelength