## Thermodynamics B/C

JT880
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### Re: Thermodynamics B/C

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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Justin72835
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### Re: Thermodynamics B/C

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?
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings."

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JT880
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Joined: June 25th, 2017, 7:16 am
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### Re: Thermodynamics B/C

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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Justin72835
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### Re: Thermodynamics B/C

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

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?
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings."

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Seven Lakes High School '19

MattChina
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### Re: Thermodynamics B/C

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

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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Justin72835
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Posts: 175
Joined: June 25th, 2017, 7:06 am
State: TX

### Re: Thermodynamics B/C

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

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.

$P=A\epsilon \sigma T^4=4\pi (0.025)^2 (0.35)(5.67*10^{-8})(4500^4-300^4)=63912 W$
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings."

University of Texas at Austin '23
Seven Lakes High School '19

MattChina
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### Re: Thermodynamics B/C

Here's another slightly remsen-esque question

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.

$P=A\epsilon \sigma T^4=4\pi (0.025)^2 (0.35)(5.67*10^{-8})(4500^4-300^4)=63912 W$
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

Solid.

MattChina
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### Re: Thermodynamics B/C

Solid.
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### Re: Thermodynamics B/C

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?