If You Put Two Similar Containers Of Water In Sunlight And Used A Lens On One Of Them...

[sandyRoe]

... would they still warm up at the same speed?

[RATTER15]

Im fairly sure the one with the correct lens and focussed correctly would heat up faster.

[jim360]

I think they would warm up at the same speed but would be worth testing. The lens might focus the heat energy better but that would also mean focusing it on a smaller part of the water -- so that while that bit heated faster there would be no extra energy added to the overall heating process. I might be wrong, though.

[society]

I agree with Methyl's explanation.

[Spoonboy]

I go with jim360.

[jim360]

Thanks -- though it would be conditional on the size of the lens too, as methyl said. Bigger lens = more energy focused on to the container = heats faster. That was the bit I've overlooked, I think.

Anyway, would depend on the lens size.

[society]

I'm sure all of you have tried the magnifying glass held in the sunlight over the hand experiment when you were a child. A larger, stronger glass give a quicker reaction than a smaller glass. Isn't this the same concept here?

[Old_Geezer]

IMO. If you are focuing radiation from a larger area than would otherwise hit the bottle, then more energy will be transferred and the water will heat faster. On the other hand if all you are doing is diverting radiation that would have hit the bottle in one position anyway to hit another position on the bottle, there will be no overall change.

[Spoonboy]

On a lighter note, unless you were some highly paid scientist with more time on their hands while dreaming up the next wow factor shocker, what purpose would it serve?! I mean, would the end of the experiment be that you drank said water from both containers, and go on from where?!!

[wildwood]

^^ ?? does the lens itself get detectably hotter diverting energy?

[jomifl]

Assuming that the lens has the same area as the profile of the bottle, most of the light would hit the lens at a right angle be focussed on an area of the bottle that would be perpendicular to the light rays so again most of those would be transmitted into the bottle. If the light was falling on a round bottlewithout using a lens the light hitting the sides of the profile would be reflected because of the shallow angle of incidence so using a lens would probably warm the bottle more quickly. If the bottle was flat then the bottle would probably absorb more light than using a lens as it would absorb equally over all its profile so all a lens would do is absorb/reflect some of the light without the advantage of focussing on a more absorbant part of the bottle. There are too many variables to give a definitive answer..

[Huderon]

It would depend on the size of the lens - there are a set of videos of cooking with a Fresnel lenses and parabolic mirrors at http://www.youtube.com/playlist?list=PL93D13BE25A7FF9E4 though the mirrors and lenses they use are big.

@Spoonboy - if you heat water from a stream or river to 65C you purify it, making it safe to drink. There is an American, non-profit, corporation showing people in developing countries how to cook their usual dishes in a solar oven which is made from silvered cardboard and lasts around 2 years. The same oven can be used to purify water as well as cook food.

[espookid]

I am actually sorry I started reading this
It is the same question i raised 50 years ago with the rain ,if you run and go faster or walk do you get wetter

[jomifl]

depends on how tall youare and how fast you run..:-)