Thermodynamics B/C

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Re: Thermodynamics B/C

Postby JT880 » February 18th, 2018, 11:34 am

Since nobody is going, I though I'd jump in!

Sorry if this is too easy: If 50.0mL of water at a temperature of 60 degrees Celsius is heated at a steady rate of 5000W, how long will it take to reach its boiling point?
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Re: Thermodynamics B/C

Postby Justin72835 » February 18th, 2018, 11:46 am

Since nobody is going, I though I'd jump in!

Sorry if this is too easy: If 50.0mL of water at a temperature of 60 degrees Celsius is heated at a steady rate of 5000W, how long will it take to reach its boiling point?
1.7 seconds?
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Re: Thermodynamics B/C

Postby JT880 » February 18th, 2018, 3:33 pm

Since nobody is going, I though I'd jump in!

Sorry if this is too easy: If 50.0mL of water at a temperature of 60 degrees Celsius is heated at a steady rate of 5000W, how long will it take to reach its boiling point?
1.7 seconds?
Correct! Guess I should have made it a bit harder. Your turn!
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Re: Thermodynamics B/C

Postby Justin72835 » February 18th, 2018, 4:09 pm

Correct! Guess I should have made it a bit harder. Your turn!
Here's another slightly remsen-esque question :D

The emissivity of tungsten is 0.350. A tungsten sphere with radius 2.50 cm is suspended within a large evacuated enclosure whose walls are at 300.0 K. What power input is required to maintain the sphere at a temperature of 4500.0 K if heat conduction along the supports is neglected?
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Re: Thermodynamics B/C

Postby MattChina » February 18th, 2018, 5:06 pm

Correct! Guess I should have made it a bit harder. Your turn!
Here's another slightly remsen-esque question :D

The emissivity of tungsten is 0.350. A tungsten sphere with radius 2.50 cm is suspended within a large evacuated enclosure whose walls are at 300.0 K. What power input is required to maintain the sphere at a temperature of 4500.0 K if heat conduction along the supports is neglected?
5.54*10^8 watts?
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Re: Thermodynamics B/C

Postby Justin72835 » February 18th, 2018, 6:34 pm

Correct! Guess I should have made it a bit harder. Your turn!
Here's another slightly remsen-esque question :D

The emissivity of tungsten is 0.350. A tungsten sphere with radius 2.50 cm is suspended within a large evacuated enclosure whose walls are at 300.0 K. What power input is required to maintain the sphere at a temperature of 4500.0 K if heat conduction along the supports is neglected?
5.54*10^8 watts?
Good try, but you may have forgotten to account for surface area or something.
If the tungsten continuously radiates away its energy then it will obviously see a decrease in temperature. Therefore, the power input is exactly equal to the net energy radiated away each second.

[math]P=A\epsilon \sigma T^4=4\pi (0.025)^2 (0.35)(5.67*10^{-8})(4500^4-300^4)=63912 W[/math]
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But in ourselves, that we are underlings."


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Re: Thermodynamics B/C

Postby MattChina » February 19th, 2018, 7:07 am

Here's another slightly remsen-esque question :D

The emissivity of tungsten is 0.350. A tungsten sphere with radius 2.50 cm is suspended within a large evacuated enclosure whose walls are at 300.0 K. What power input is required to maintain the sphere at a temperature of 4500.0 K if heat conduction along the supports is neglected?
5.54*10^8 watts?
Good try, but you may have forgotten to account for surface area or something.
If the tungsten continuously radiates away its energy then it will obviously see a decrease in temperature. Therefore, the power input is exactly equal to the net energy radiated away each second.

[math]P=A\epsilon \sigma T^4=4\pi (0.025)^2 (0.35)(5.67*10^{-8})(4500^4-300^4)=63912 W[/math]
yes i forgot to mulitply by the stefan-Boltzmann constant and I misread cm as m.

I guess ill ask a question now.
Which state of water has the highest value of thermal conductivity?
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Re: Thermodynamics B/C

Postby UTF-8 U+6211 U+662F » February 22nd, 2018, 5:56 pm

Solid.

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Re: Thermodynamics B/C

Postby MattChina » February 23rd, 2018, 6:40 am

Solid.
Correct. your turn
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Re: Thermodynamics B/C

Postby UTF-8 U+6211 U+662F » February 23rd, 2018, 5:19 pm

What is the term for a process that occurs
a) at constant pressure?
b) at constant volume?
c) at constant temperature?
d) without transfer of heat in or out?
e) in a way such that the macrostates are constantly defined?
f) in a way such that the system can return to its exact previous state?
g) with no change of entropy?
h) as a series of multiple processes that put the system back to its original state?
i) with a constant PV^n where n is any real number?


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