Physics

Flying

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Wheeeeee!

Wheeeeee!

No, not with wings, not in an aeroplane

I mean skydiving without a parachute. Like superman.

If you ever drop past Singapore you really should give it a go. It’s on Sentosa.

Update: now there’s one in Sydney too!

20140329_194913

Building Fibre lasers

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So the other day I got to build a fibre laser (hence the cool colours in the picture above). Technically it’s just an amplifier, it needs some input light, and it makes more of it.

So you feed in 0.006 Watts of seed light at one end, and out the other end of the optical fibre you get 5 Watts. This is all invisible light in the infrared.

Where does the extra energy come from, you say? Well. You also put in a whole lot of light of a different colour. That’s the red looking light above. You can’t see it with your eyes (nor would you want to, it could blind you), but your camera can probably see it. We put in 10 Watts of this light.

The mixture of chemicals which have been put into the glass which makes up the optical fibre, allow the pump light (red) to be absorbed, and the seed light (invisible) to be amplified.

But they do other things too. They can absorb two photons of pump light (red), and emit a photon with twice the energy (green in the photo). This is known as frequency doubling. Sometimes you want this, but not here. Here it is just a loss mechanism. But a very pretty loss mechanism none the less.

 

 

 

Surface Tension and Viscosity

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Blue_drip

The other day I found myself wondering if surface tension is related to viscosity. Turns out it is, with a precise exponential relationship for any given liquid. Of course both depend upon temperature implicitly, with viscosity and surface tension becoming small near the boiling point, and being large near the freezing point.

gamma is surface tension eta is viscosity

Relation between surface tension and viscosity for a given fluid. Gamma is surface tension.
Eta is viscosity, for the liquid (l) or for the gas (g). A, B and Eta(g) are constants for each fluid.

Source:

“Surface Tension-Viscosity Relationship for Liquids.” 
Harold Schonhorn J. Chem. Eng. Data, 1967, 12 (4), pp 524–525
DOI: 10.1021/je60035a016
Publication Date: October 1967
Link: http://pubs.acs.org/doi/abs/10.1021/je60035a016