## Thermodynamics B/C

Justin72835
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### Re: Thermodynamics B/C

Way to ruin the fun

Jk haha, that's the right answer. Go ahead with the next question!
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings."

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### Re: Thermodynamics B/C

There is a uniform sphere that can be approximated as being a blackbody. The sphere has a radius of 20 cm and has a temperature of 4300 K. The temperature of the surroundings is 300 K.

Find the rate of heat transfer between the sphere and the surroundings.

If you wanted to halve the rate of heat transfer, then what should you change the temperature of the sphere to?
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Justin72835
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### Re: Thermodynamics B/C

There is a uniform sphere that can be approximated as being a blackbody. The sphere has a radius of 20 cm and has a temperature of 4300 K. The temperature of the surroundings is 300 K.

Find the rate of heat transfer between the sphere and the surroundings.

If you wanted to halve the rate of heat transfer, then what should you change the temperature of the sphere to?
"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

Alex-RCHS
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### Re: Thermodynamics B/C

There is a uniform sphere that can be approximated as being a blackbody. The sphere has a radius of 20 cm and has a temperature of 4300 K. The temperature of the surroundings is 300 K.

Find the rate of heat transfer between the sphere and the surroundings.

If you wanted to halve the rate of heat transfer, then what should you change the temperature of the sphere to?
This feels more like Remote to me, but
Edit: beat me to it. Please note my point about the phrasing of the question, though.
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### Re: Thermodynamics B/C

There is a uniform sphere that can be approximated as being a blackbody. The sphere has a radius of 20 cm and has a temperature of 4300 K. The temperature of the surroundings is 300 K.

Find the rate of heat transfer between the sphere and the surroundings.

If you wanted to halve the rate of heat transfer, then what should you change the temperature of the sphere to?
This feels more like Remote to me, but
Edit: beat me to it. Please note my point about the phrasing of the question, though.
Correct me if I'm wrong, but how can the two objects be in thermodynamic equilibrium when they are at different temperatures? For example, lets say that a hot piece of coal (which is we can approximate as a blackbody) was left out at room temperature, it will continuously cool down until it reaches thermodynamic equilibrium with its surroundings.

PS - A friend that does remsen actually helped me write this, since I don't actually do this event, so sorry if it's a bit off topic xD
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Alex-RCHS
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### Re: Thermodynamics B/C

Correct me if I'm wrong, but how can the two objects be in thermodynamic equilibrium when they are at different temperatures? For example, lets say that a hot piece of coal (which is we can approximate as a blackbody) was left out at room temperature, it will continuously cool down until it reaches thermodynamic equilibrium with its surroundings.
Well, first of all, I was wrong about what I said earlier, my apologies. I think that one requirement for black body *radiation* to occur is that the black body is in thermal equilibrium with its surroundings, but I don’t think that’s a requirement for something to simply *be* a black body. But I could be wrong about that.

Anyways, since you said to approximate it as a black body then there’s no reason to assume that the object is in thermodynamic equilibrium with its surroundings, so that’s my bad.

Also, they could be in thermodynamic equilibrium at different temperatures because of radiation, but in this case that wouldn’t occur because the hotter object has a higher emissivity (and because the difference in temperatures wasn’t so large).
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### Re: Thermodynamics B/C

There is a uniform sphere that can be approximated as being a blackbody. The sphere has a radius of 20 cm and has a temperature of 4300 K. The temperature of the surroundings is 300 K.

Find the rate of heat transfer between the sphere and the surroundings.

If you wanted to halve the rate of heat transfer, then what should you change the temperature of the sphere to?
University of California at Berkeley '23
Seven Lakes High School '19
Seven Lakes Junior High '15

Justin72835
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### Re: Thermodynamics B/C

There is a uniform sphere that can be approximated as being a blackbody. The sphere has a radius of 20 cm and has a temperature of 4300 K. The temperature of the surroundings is 300 K.

Find the rate of heat transfer between the sphere and the surroundings.

If you wanted to halve the rate of heat transfer, then what should you change the temperature of the sphere to?
A pressure gauge indicates the differences between atmospheric pressure and pressure inside the tank. The gauge on a 2.00 m^3 oxygen tank reads 36 atm. After some use of the oxygen, the gauge reads 24 atm. How many cubic meters of oxygen at normal atmospheric pressure was used? There is no temperature change during the time of consumption.
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings."

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### Re: Thermodynamics B/C

A pressure gauge indicates the differences between atmospheric pressure and pressure inside the tank. The gauge on a 2.00 m^3 oxygen tank reads 36 atm. After some use of the oxygen, the gauge reads 24 atm. How many cubic meters of oxygen at normal atmospheric pressure was used? There is no temperature change during the time of consumption.

Justin72835
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### Re: Thermodynamics B/C

A pressure gauge indicates the differences between atmospheric pressure and pressure inside the tank. The gauge on a 2.00 m^3 oxygen tank reads 36 atm. After some use of the oxygen, the gauge reads 24 atm. How many cubic meters of oxygen at normal atmospheric pressure was used? There is no temperature change during the time of consumption.
Not quite
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings."

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### Re: Thermodynamics B/C

A pressure gauge indicates the differences between atmospheric pressure and pressure inside the tank. The gauge on a 2.00 m^3 oxygen tank reads 36 atm. After some use of the oxygen, the gauge reads 24 atm. How many cubic meters of oxygen at normal atmospheric pressure was used? There is no temperature change during the time of consumption.
Not quite
Oh, whoops. Next question: If a Carnot engine operates at 50 degrees Fahrenheit and 80 degrees Fahrenheit, find the change in entropy after one cycle. What would be the change in entropy if the Carnot engine were a Carnot refrigerator? Explain why the Carnot engine is the most efficient heat engine between two temperature sources.

Justin72835
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### Re: Thermodynamics B/C

Not quite
Oh, whoops. Next question: If a Carnot engine operates at 50 degrees Fahrenheit and 80 degrees Fahrenheit, find the change in entropy after one cycle. What would be the change in entropy if the Carnot engine were a Carnot refrigerator? Explain why the Carnot engine is the most efficient heat engine between two temperature sources.
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings."

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### Re: Thermodynamics B/C

Not quite
Oh, whoops. Next question: If a Carnot engine operates at 50 degrees Fahrenheit and 80 degrees Fahrenheit, find the change in entropy after one cycle. What would be the change in entropy if the Carnot engine were a Carnot refrigerator? Explain why the Carnot engine is the most efficient heat engine between two temperature sources.
Yep! Although you could explain the last part a little more (non sequitur there). Your turn!

Justin72835
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### Re: Thermodynamics B/C

Oh, whoops. Next question: If a Carnot engine operates at 50 degrees Fahrenheit and 80 degrees Fahrenheit, find the change in entropy after one cycle. What would be the change in entropy if the Carnot engine were a Carnot refrigerator? Explain why the Carnot engine is the most efficient heat engine between two temperature sources.
Yep! Although you could explain the last part a little more (non sequitur there). Your turn!
Alright. A cup of tea cools from 170 degrees Fahrenheit to 145 degrees Fahrenheit in 6 minutes in a room at 72 degrees Fahrenheit. How long will it take for the tea to cool from 100 to 90 degrees Fahrenheit in the same room?
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings."

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### Re: Thermodynamics B/C

Alright. A cup of tea cools from 170 degrees Fahrenheit to 145 degrees Fahrenheit in 6 minutes in a room at 72 degrees Fahrenheit. How long will it take for the tea to cool from 100 to 90 degrees Fahrenheit in the same room?