Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: ENERGY WITH Q PLEASE VOTE



On Wed, 14 Nov 2001, Robert Cohen wrote:

Could someone give an accounting for the following two scenarios?

1. A box has two parts of equal volumes. One compartment is empty (vacuum).
By turning a small number, the gas in the other compartment is allowed to
expand into the empty compartment.

What is W?
What is Q?
What is deltaE?
What is deltaT?

It depends. If it is an ideal gas, delta E and delta T are both
zero. If it is a real gas delta E is zero but delta T probably is
not. *I* would say that W and Q are both zero, but if somebody
wanted to argue differently I wouldn't waste any time on it since
it would have no physical consequence.

2. The box is then raised a height H.

What is W?
What is Q?
What is deltaE?
What is deltaT?

Now it depends on your definition of work. Some definitions (like
one that we encounter in the mechanics section of the text) lead
to W = delta E = Mgh. Others (like one we encounter in the
thermal physics section of the text) lead to W = delta E = ~0.

Again I would say Q = 0. And as long as the box is lifted gently
from the original height to the final height, delta T ~= 0 as
well.

John Mallinckrodt mailto:ajm@csupomona.edu
Cal Poly Pomona http://www.csupomona.edu/~ajm