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Hope this makes sense. I would appreciate any lucid responses
that can reduce my confusion about what is Ordered form of Energy
& what is not.

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On 2005-09-03, gsax <gaurav_iitg@yahoo.com> wrote:

Hi

Entropy is defined as:
" A measure of the disorder or randomness in a closed system"

Alternatively it is also defined as
:"For a closed thermodynamic system, a quantitative measure of the
amount of thermal energy not available to do work."

I am not sure how one definition follows from the other & how are they
equivalent.

It's a very good question. This equivalence is far from obvious. It is
the great achievement of Boltzmann and other founders of statistical
mechanics.

If Heat is "Disordered form of Energy" , then what are the "Ordered
forms".
You may say ...light.

Actually, I was going to say mechanical energy. Examples include
kinetic energy, the potential energy of a pendulum, the compression
energy or a spring, or the work that can be done by a gas exerting a
pressure on a piston. These are forms of energy that we can directly
exploit. If a source of such energy is available, it is a simple matter
to rig up some pulleys and gears to use this energy to, say, make an
elevator work.

From the experiments of Joule and others, we know that this kind of
mechanical work can be turned into heat. But, can heat be turned back
into mechanical work? Intuitively, it's clear that that's not so easy.
It's kind of hard to power an elevator with a hot piece of rock. One has
to use a medium that can convert thermal energy into mechanical energy,
such as a gas which expands when heated, or a thermoelectric device that
produces a current under a temperature gradient.

The empirical study of such "converter" media has resulted in the
formulation of thermodynamics and the identification of entropy, which
quantifies how much thermal energy cannot be extracted as mechanical
work. The great achievement of Boltzmann was to calculate this quantity
based on a microscopic theory of the material in question. He calculated
it precisely as the "amount of disorder" in the microscopic
configuration of the material.

But then any hot body also radiates EM waves & then could be said to be
producing "Ordered Energy" (Light) from "Disordered Energy" (Heat)...

Alternatively what is the Entropy of a collection of Light Quanta?

Radiation, just like matter, can be treated thermodynamically. Also,
contrary to what you seem to be thinking, radiation is not energy, it
can store energy. Just like an ideal gas of molecules, a bunch of
photons bouncing around in a box behave like an ideal gas. It has the
same equation of state, pV = NT (Boltzmann's constant set to 1), but a
different internal energy, U = 3NT, as opposed to U = (3/2)NT for a
non-relativistic monatomic gas. Just like a regular gas, it has pressure
that can do mechanical work as well as entropy, which quantifies the
amount of work that can be extracted from it, as you said above.

Hope this makes sense. I would appreciate any lucid responses that can
reduce my confusion about what is Ordered form of Energy & what is not.

The short answer is mechanical energy (available to do mechanical work),
and sometimes chemical energy (available to change the number of
molecules of a particular species). There are other examples, of various
degrees of sophistication, but these are the most common ones. The rest
is heat, or so-called disordered energy.

Hope this helps.

Igor