Hi.

In a sunny day you can easily make a fire by using a lens. What is the
biggest theorethical temperature you can get by using a lens?

Krzysztof Geras
Please answer on my private adress if possible.

On Sun, 07 Sep 2003 15:54:30 -0400, Krzysztof Geras wrote:

Hi.

In a sunny day you can easily make a fire by using a lens. What is the
biggest theorethical temperature you can get by using a lens?

Krzysztof Geras
Please answer on my private adress if possible.

You can't passively make heat flow from hot to hotter. So a first order
estimate at the upper limit of the temperature must be less that that of
the sun.

Krzysztof Geras wrote:

Hi.

In a sunny day you can easily make a fire by using a lens. What is the
biggest theorethical temperature you can get by using a lens?

By the First Law of Thermodynamics, the temperature of a focus cannot
exceed the temperature of the emission source.

Note that a lasing medium, operating from a population inversion, has
a negative temp kelvin that is hotter than any positive temp kelvin.
Coherent in time and space TEM_00 monochromatic light can be focused
to a 1/2 wavelength Airy circle and thermometer temp has nothing to do
with it. Thus we obtain the naughty things folks do with really big
high power multiple beam lasers and holoraums in inertial confinement
fusion.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
"Quis custodiet ipsos custodes?" The Net!

In article , (Krzysztof Geras) writes:
Hi.

In a sunny day you can easily make a fire by using a lens. What is the
biggest theorethical temperature you can get by using a lens?

The source temperature (for source and image embedded in an
environment with the same refraction coefficient).

Mati Meron | "When you argue with a fool,
| chances are he is doing just the same"

wrote:
: The source temperature (for source and image embedded in an
: environment with the same refraction coefficient).

What does that mean? Actually, a solar furnace
was built in Europe 50 years ago that produced temperatures
about twice the temperature of the surface of the sun.

But it was mirrors, not a lens.

Joe Fischer

--
3

In article , Joe Fischer writes:
wrote:
: The source temperature (for source and image embedded in an
: environment with the same refraction coefficient).

What does that mean?

Just what it says.

Actually, a solar furnace
was built in Europe 50 years ago that produced temperatures
about twice the temperature of the surface of the sun.

Nope.

But it was mirrors, not a lens.

No matter, the answer is still "nope". If you'll learn some physiscs,
you'll be much less prone to swallow fairy tales.

Mati Meron | "When you argue with a fool,
| chances are he is doing just the same"

"Joe Fischer" wrote in message
...
wrote:
: The source temperature (for source and image embedded in an
: environment with the same refraction coefficient).

What does that mean? Actually, a solar furnace
was built in Europe 50 years ago that produced temperatures
about twice the temperature of the surface of the sun.

But it was mirrors, not a lens.

Joe Fischer

--
3

Didn't happen... don't care if they used mirrors
as big as planets all focusing on a gigantic
lens 10000 miles across focused on a ants
ass ...

In sci.physics, Paul R. Mays

wrote
on Mon, 8 Sep 2003 02:09:18 -0400
:

"Joe Fischer" wrote in message
...
wrote:
: The source temperature (for source and image embedded in an
: environment with the same refraction coefficient).

What does that mean? Actually, a solar furnace
was built in Europe 50 years ago that produced temperatures
about twice the temperature of the surface of the sun.

But it was mirrors, not a lens.

Joe Fischer

--
3

Didn't happen... don't care if they used mirrors
as big as planets all focusing on a gigantic
lens 10000 miles across focused on a ants
ass ...


How could they measure that ass if it kept getting fried by
the beams? Even if it only gets, say, half the temperature
of the Sun (1/2 of 5800K, or 2700 K) it's still hot enough
to melt iron (and almost hot enough to boil it), and fry
most carbon-based lifeforms, ants among them.

:-)

I'll admit to some curiosity as to whether they made the tower
out of tungsten, which has a boiling point of 5828 K. (The
melting point is 3695 K.) Since the surface of the Sun is
estimated to be 5800 K it's barely possible (though unlikely)
that there's liquid tungsten on the Sun's surface, though it
depends on the gas pressure.

The only element with a higher boiling point is rhenium
(5869K). If they did achieve twice the sun's temperature,
or even just the sun's temperature, there wouldn't be much
left of that bit of the tower.

Ants included. :-)

--
#191,
It's still legal to go .sigless.