# Isobaric, Isochoric, Isothermal, and Adiabatic Processes

http://session.masteringphysics.com/problemAsset/1013990/12/1013990E.jpg

Which of the following statements are true about the first half of this process, just going from
state A to state F?

Both T and U increase.
W provides energy input.
Q provides energy input.
Q is larger (in magnitude) than W.

I know that Q provides energy input, but none of the other ones sound corrects to me. . .

please help.

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## Answers and Replies

OK. Here's how to approach this:

1) Is there an increase or decrease in temperature, and hence is there an increase or decrease in U? (Hint: Think ideal gas eqn.)
2) Is there any work done on or by the gas? How do you know?
3) Relate the signs and magnitudes of U and W, to the sign and magnitude of Q by the first law of thermodynamics.

Andrew Mason
Science Advisor
Homework Helper
Which of the following statements are true about the first half of this process, just going from
state A to state F?

Both T and U increase.
W provides energy input.
Q provides energy input.
Q is larger (in magnitude) than W.
I will assume this is an ideal gas. The PV graph shows P declining linearly as V increases. Plot the isotherm (ie a path in which T is constant: ie P = nRT/V). Now what can you say about paths that are ABOVE the isotherm and paths that are below it (ie what happens to the temperature jn moving along the path?). Is A-F above or below the isotherm?

Now plot the adiabatic path:

$$PV^\gamma = K$$

What can you say about Q on the adiabatic path? What can you say about a path that is above the adiabatic path? Below? Is A-F above or below the adiabatic path? What does that tell you about Q?'

Now consider the work done from A-F. How do you measure that? How does that compare to the work done with the adiabatic path? (Q=0). What does that tell you about the work done compared to heat flow?

AM