Re: Question about light and heat

["John S. Denker" <jsd@MONMOUTH.COM>]

Tina Fanetti wrote:
> HUH?
> I am looking in Halliday, Resineck and Walker and it says that heat
> is transferred internal energy.  Is this not saying heat is energy?

It depends on what the definition of "is" is.  Sorry!

In English, sometimes
        A is B
means
        A is identically equivalent to B
and at other times it means
        A is an example of B, or a form of B, or a subset of B.


In my book, heat is (exactly, by definition) thermal energy.
So heat is a form of energy.  I would avoid saying heat "is"
energy, for fear of being misunderstood, but if somebody else
made such a statement in the proper context, I wouldn't throw
a fit about it.

Focussing attention on "transfers" of energy is a blunder,
for several reasons as documented at
  http://www.monmouth.com/~jsd/physics/thermo-laws.htm
and using heat to refer to this notion is objectionable
(not because of the word, but because of the notion).

===============

To return to the original question, I would not say light
"is" energy.  Light is (exactly, by definition) electromagnetic
radiation, especially (by connotation) EM radiation in the
visible band.  Light carries energy.  (It also carries other
things, like momentum.)  (It is by no means the only carrier
of energy.)

Radiant heat is a form of electromagnetic radiation.  (It
is by no means the only form of heat.)