# Refraction question!

1. Jul 23, 2008

### RagingPineapple

I have a question!!

On my desk is a aerosol of compressed air, for blowing dust away and stuff.

If you look carefully, the jet stream of air causes a visible refraction against the background. Why is this?

I'm assuming it's based on the same way that a heat-haze causes refractions over roads and cars.

2. Jul 23, 2008

### mgb_phys

Yes it's similair - the refractive index of a gas depends on it's pressure.
On the road the hot air has lower pressure than the surroundings, making a lens.
In the compressed air can the expanding compressed gas has a differnet density to the room air.

3. Jul 23, 2008

### RagingPineapple

So taking into account the refractive index of any transparent container it would require, would it be possible to create a lens with a specific refractive index simply by creating a shaped container of pressurised gas/liquid?

Just curiosity really :)

Like with water, if it were possible to forcibly inject water into an already full container, thereby compressing what was already there, would you visibly see the refractive index of the water start to alter as the volume in the tank increased?

4. Jul 23, 2008

### mgb_phys

Yes - it would be fairly slow to respond though.
Water doesn't compress much so there isn't a big change in refractive index with pressure - it does change with temperature or other stuff disolved in it. If you add vodka/gin to water you can see the difference in refractive index as they mix.

The techniqueis uesed the other way around to measure density of a material.
It's easy optically to measure extremely small differences in refractive index and this is used to determine the concentration of things like salt/sugar in a liquid or to match a sample of glass by putting it in a tank of oil and heating the oil until it matches the refractive index of the glass.