Bulb Used As Convex Lens

[thinhnghiem]

Dear all
I have used a bulb which is filled in with water, it works like a convex lens to concentrate solar energy.
The performance of the water bulb gets highest level when I incline the bulb like in the clip. Solar light beam focus on a bigger dot, in compared with the dot when let the bulb standing vertically.

See my clip at

https://www.youtube.com/watch?v=f0Nvc6Q_Ulw

[exchemist]

Dear all

I have used a bulb which is filled in with water, it works like a convex lens to concentrate solar energy.

The performance of the water bulb gets highest level when I incline the bulb like in the clip. Solar light beam focus on a bigger dot, in compared with the dot when let the bulb standing vertically.

 

See my clip at

 

https://www.youtube.com/watch?v=f0Nvc6Q_Ulw

Yes, you are producing a caustic pattern. You could do the same with a drinking water glass, though since the refracting medium would in that case be cylindrical, rather than close to spherical, the shape would not be quite the same. 

 

More about caustics here: https://en.wikipedia.org/wiki/Caustic_(optics)

 

Until I read this I did not realise that the term "caustic" is from the Greek for "burnt", which explains why the same term is perhaps more familiar in a chemistry context, e.g. "caustic soda" is one old name for the strong alkali, sodium hydroxide, NaOH.  We learn something every day :)