- #1
bryanso
- 28
- 7
Hi, there is no other topics in my adventure in Feynman Lectures that makes me so loss in thoughts (https://www.feynmanlectures.caltech.edu/I_44.html). I seem to understand every sentence. But the whole thing is completely unintelligible. Let me start by asking one fundamental question. I am sure after that I would have a lot more. Thanks for support.
This question is about "magical assumptions". So Mr. Feynman assumes we have an ideal engine with no friction, I'm fine with that. Now he assumes there are two magical "heat pads" at temperature T1 and T2.
https://www.feynmanlectures.caltech.edu/img/FLP_I/f44-06/f44-06_tc_big.svgz
At point (c) he wrote,
The gas cylinder has now reached the temperature T2, so that if we put it on the heat pad at temperature T2 there will be no irreversible changes. Now we slowly compress the gas while it is in contact with the reservoir at T2, following the curve marked (3) (Fig. 44–5, Step 3). Because the cylinder is in contact with the reservoir, the temperature does not rise, but heat Q2 flows from the cylinder into the reservoir at the temperature T2.
This question is about "magical assumptions". So Mr. Feynman assumes we have an ideal engine with no friction, I'm fine with that. Now he assumes there are two magical "heat pads" at temperature T1 and T2.
https://www.feynmanlectures.caltech.edu/img/FLP_I/f44-06/f44-06_tc_big.svgz
At point (c) he wrote,
The gas cylinder has now reached the temperature T2, so that if we put it on the heat pad at temperature T2 there will be no irreversible changes. Now we slowly compress the gas while it is in contact with the reservoir at T2, following the curve marked (3) (Fig. 44–5, Step 3). Because the cylinder is in contact with the reservoir, the temperature does not rise, but heat Q2 flows from the cylinder into the reservoir at the temperature T2.
- Everything else is assumed to be ideal... I would think if heat Q2 flows from the cylinder into the reservoir at temperature T2 then obviously the reservoir's temperature would start to increase too? Why can he make such an assumption that it doesn't?
- It seems like he's making assumptions here and there that just happen to work with his argument, quite arbitrarily.
- He said "we slowly compress the gas while it is in contact with the reservoir at T2". But later on, all the calculation seems to ignore there are "external work"... done by "we". Why is that left out?