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Re: COLLISION 2



At 13:36 11/29/99 -0700, Jim wrote:

A photon leaves the sun with h-nu of energy, travels through
space, strikes the surface of the earth and is absorbed by an atom.

Questions:
1) Didn't the internal energy of the sun decrease (change) by
h-nu?

I don't know how helpful it is to think of a "photon" as a real particle,
but let's do for the nonce -- yes, something in the sun did work on this
assumed particle and increased its energy and at the same time work was
done on the sun to decrease the energy there.

2) Didn't the internal energy of the earth increase (change) by
h-nu?
As the "photon" collides with the Earth it does indeed do work on the
Earth and the internal energy does indeed increase.///

Jim Green

This is the clearest statement of Jim's position on heat vs work that I
have seen.

In considering the various gradations between conduction, convection and
radiation, I fancy Jim would see a hot plate in contact with a water
container as heating the water.

I reckon Jim might allow that if the contact method were to be replaced
by a gas flame playing hot air on the water pot, it would yet be heating
the water.

But if a 'heat' lamp replaces the gas flame or the hotplate, then it
seems this is not heating but working the water into boiling...
...because there is no physical contact with a higher temperature
reservoir.

If this same heat lamp were placed beneath the water pot, and played
on a plate in contact with the pot, then the pot would be heated
even though the (radiatively heated) plate was worked.

I think I have it!

But wait: the metal base of the pot can serve as the radiative
absorber, so I suppose that the water can still be heated by the pot,
though the pot is worked by the heat lamp?




brian whatcott <inet@intellisys.net>
Altus OK