Thermodynamics B/C

[pikachu4919]

Hey guys...I was solving a thermo test and came across this question:

If Th = 30°C and Tc =230°C, what is the maximum efficiency?

I used the equation 1 - Tcold/Thot and I got 0.87 (rounded) which was one of the answer choices. The correct answer however was 0.40.

Can anyone explain this to me (or attach a link that does?)

(Or is it that the answer key was wrong?)

You should use degrees Kelvin for calculations like this.

Yeah I got ~0.4 after plugging it in Kelvin. Nonetheless, that is, to some extent, the correct formula for efficiency.

[arv101]

Anyone know a good place to find practice problems?

[Alex-RCHS]

Anyone know a good place to find practice problems?

This was an event in the 2012 and 2013 seasons, so there should be tests on the test exchange (although you're advised to find the old rules, if possible, to be sure the topics covered are the same).

Also, your signature doesn't seem to be working quite right, although it's very funny.

[Justin72835]

Anyone know a good place to find practice problems?

Honestly, I think the best way to practice thermo is by doing problems in textbooks. Most practice problems online are either really easy or really hard. With that said, Giancoli has some pretty good problems at the ends of its chapters. For harder stuff, you can look into textbooks like Fundamentals of Physics or University Physics to really test your theory (although they may require at least a basic knowledge of calc). You can probably find PDFs of all these textbooks online so don't worry about spending a ton of money to buy them.

[arv101]

How are you guys heating up water to the exact degree to test your devices?, (Or how do you plan too?). I haven't tried yet but I feel like boiling the water would be to inaccurate.

[WhatScience?]

Is there anyway we can have a mock run of this event or at least for the written test?Just to see where we are?

I have a plan that I am more than happy to implement

1. First, the mock competition will take place on the weekend of Nov 18-19.

2. Anyone interested should all sign up

3. All those who sign up must write a 12 question test with an answer key.

4. Submit all those tests to me by November 15/16.

5. On Friday, November 17, I will pm the tests to all those who signed up.

6. Through the weekend, take all the tests.

7. Submit all your scores. I will average them all, (with everyone being exempt from the test they wrote.)

[I trust that nobody will cheat as this is to gauge your level. There is nothing to be gained from cheating.]

8. Placings will be released.

9. All the tests will be released.

So this way, the tests make it onto the test exchange benefiting everybody but one must submit a test to get access to the actual competition.

What do y'all think?

PM me with your name to sign up saying "I, [insert name here] sign up for the november scioly.org thermo competition.

Send your tests to whatsciencescioly@gmail.com

Remember that this is still on people

[wzhang5460]

When is the deadline for this competition?

Thanks

[arv101]

That sounds great! I was also wondering if you or someone you know could do this for hovercraft?

[WhatScience?]

When is the deadline for this competition?

Thanks

All of them are in my above post. Tests should come in to me 15th/16th. Tests pm'd to those who submitted 17th evening. Get back your scores by 19th evening. Scores and placings (anonymous...only you know your place but everyone's score without name will be released) will come out shortly after.

[Alex-RCHS]

For those using aerogel: are you worried at all about long-term viability? Since it is a powerful dessicant, I feel that it shouldn't be exposed to the humid air in the device. What do you all think?