Carnot cycle, heat and monatomic ideal gas

1. Mar 5, 2004

frznfire219

Hi, I would appreciate any help with this:

A monatomic ideal gas is used as the working substance for
the Carnot cycle. Processes A => B and C => D
are isothermal, while processes B => C and D => A are adiabatic.
During process A => B, there are 400 J of work done by the gas on
the surroundings. How much heat is expelled by the gas during process C => D?

So I'm completely stuck, all I know is that it's less than 400 J, obviously.
There's a picture of the corresponding PV graph actually at http://www.compadre.org/psrc/evals/Physics_Bowl_2003.pdf (page 12).

Thanks for any help!!

2. Mar 7, 2004

anyone?

3. Mar 7, 2004

Moose352

I'm not sure about this explanation, but whatever. You know that the carnot cycle runs at perfect efficiency ie. 1-(Ql/Qh) and you know that efficiency of the carnot cycle is also 1-(Tl/Th). I get 100 J.

4. Mar 8, 2004

frznfire219

Thanks! I actually figured it out later with the adiabatic equation (PV^gamma is constant) but your way is much more elegant.