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Can You Answer This Question ?


Integza

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Can you correctly answer this question?

 

Imagine this, you put a refrigerator with his door open in a completely thermally insulated room, what means this room doesn’t allow heat transfer from the inside to the outside and vice-versa .

 

The question is the following, after 10h what will happen to the room’s temperature?

 

Will the room be colder? Hotter? Or at the same temperature?

 


 

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If you like to understand the physical world around you in a funny manner, visit my channel:


 

The question that inspired this video was found in an awesome forum about Mechanical engineering:


 

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Nice. Reminds of of this:

You're making a hot drink and somebody knocks on your door. You've just poured boiling water into the mug. You don't want the drink to be too cool when you come back to it, so you need to decide whether it would be better to pour the milk in now or when you come back.

A. Don't pour the milk in yet.

B. Pour it in now.

C. It makes no difference, the temperature loss will be the same.

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Hi :D

 

Just saw your reply and looks like a good one.

 

Here is my guess...

 

This problem is all about heat transfer , and knowing that the time is the same in all three cases the most important thing is the rate at which energy is lost.

We also know that  in the three cases the initial amount of energy of the water is the same.

 

In the this case the water can lose energy in two ways, by convection and by evaporation (latent heat), the question here is how the milk affect these.

 

I think the way the water would lose more heat his by evaporation, by pouring milk right away we would be decreasing the temperature of the mixture just enough so the water would evaporate in a  slower manner, losing less heat in this way.

 

By convection Q=h*A*dT, well we would increase the area to heat to be transfered through  but we also would decrease the temperature diference so i think it would not affect that much in this way, we would also be increasing the mass of the mixture what means it would be harder to lose heat because of the increase on the "thermal inertia".

 

This is my wild guess on the top of my head right now, to be sure i think i would need to investigate a little more .

 

If i'm wrong please don't tell me why, i want to find out :D

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Have you done the Monty Hall problem?

You're on a gameshow and the host shows you three doors and asks you to pick one. Behind one of the doors is the jackpot prize. You pick a door and the host then eliminates one of the doors that doesn't have the prize and asks you if you want to stick to your original choice or switch to the other door. Do you...

A. Stick with the same door.

B. Switch to the other door.

C. It makes no difference.

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Oh and if you were to mention that my channel is intended mainly for instruction, including for complete beginners and tutorials will be coming very soon (when my knee heals) that would be super awesome. :)

I've got a couple more for you that are pure logic and/or mathematics like the Monty Hall one.


Two prisoners are being held for a crime that the didn't commit. The verdict is that the judge can't be sure so him gives them a 50/50 chance of being set free. If at least one of them goes free they can prove the innocence of both of them. In the morning both prisoners are going to be lead out into the yard blindfolded. The blindfolds will be removed after they've each had either a blue or a white hat placed on the head. If they can guess the colour of their own hat that prisoner will be set free. The night before they figure out a way for one of them to definitely go free. How did they do it? There's two of each colour hat available so it's not as simple as that.


And a really simple one. Somebody needs to buy birthday cards for twin children of their friend and the need to know the gender of both twins to buy appropriate cards. They know for a fact that they're not both girls. Do they stand a better chance of getting it right if they...

A. Buy one boy's card and one girls card.

B. Buy two boy's cards.

C. It makes no difference, the odds are the same.

Edited by A-wal
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Can you correctly answer this question?
 
Imagine this, you put a refrigerator with his door open in a completely thermally insulated room, what means this room doesn’t allow heat transfer from the inside to the outside and vice-versa .
 
The question is the following, after 10h what will happen to the room’s temperature?
 
Will the room be colder? Hotter? Or at the same temperature?
 
 

 

That is, without a doubt, the stupidest question I have ever heard. Clearly, you have not specified the original temperature of the room nor he volume of the room (relative to the refrigerator), the central perimeters of interest. If the room is colder than the temperature set for the refrigerator, the refrigerator will shut off and the temperature of the combination will lower to some point between the two; i.e., the the volume ration sets the final temperature.

 

If the room is hotter than the temperature set for the refrigerator, the refrigerator will run, putting off heat.  The result is ever increasing heat until the mechanism controlling the refrigerator fails at which time the whole thing fails to continue.

 

God why do people make such stupid posts to this forum? 

Edited by Doctordick
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That is, without a doubt, the stupidest question I have ever heard. Clearly, you have not specified the original temperature of the room nor he volume of the room (relative to the refrigerator), the central perimeters of interest. If the room is colder than the temperature set for the refrigerator, the refrigerator will shut off and the temperature of the combination will lower to some point between the two; i.e., the the volume ration sets the final temperature.

 

If the room is hotter than the temperature set for the refrigerator, the refrigerator will run, putting off heat.  The result is ever increasing heat until the mechanism controlling the refrigerator fails at which time the whole thing fails to continue.

 

God why do people make such stupid posts to this forum? 

I think the exact same thing when I see posts like that one.

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That is, without a doubt, the stupidest question I have ever heard. Clearly, you have not specified the original temperature of the room nor he volume of the room (relative to the refrigerator), the central perimeters of interest. If the room is colder than the temperature set for the refrigerator, the refrigerator will shut off and the temperature of the combination will lower to some point between the two; i.e., the the volume ration sets the final temperature.

 

If the room is hotter than the temperature set for the refrigerator, the refrigerator will run, putting off heat.  The result is ever increasing heat until the mechanism controlling the refrigerator fails at which time the whole thing fails to continue.

 

God why do people make such stupid posts to this forum? 

 Hi there.

First i would like to thank you  for the time you took to make that post.

 

I think you my friend lack common sense, this question has the sole purpose of making science fun.

 

You would be right if this question was a problem in an engineering exam but is not, is just a  normal question in which a person with common sense has the ability to know the refrigerator is neither in the north pole or the burning flames of hell. Is just a normal refrigerator in a room at ambient temperature, working with is door  open.

 

Analysing everything by the degree of specification you ask would make everything look stupid.

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That is, without a doubt, the stupidest question I have ever heard.

:Exclamati: DrDick, your post constitutes rude and offensive behavior, which violates our site rules. Please don’t be rude and offensive!

 

 

Imagine this, you put a refrigerator with his door open in a completely thermally insulated room, what means this room doesn’t allow heat transfer from the inside to the outside and vice-versa .

 

The question is the following, after 10h what will happen to the room’s temperature?

 

Will the room be colder? Hotter? Or at the same temperature?

As you say in your YouTube video’s, Integza, I say, assuming the refrigerator is a typical kind, has power, and is set to maintain a temperature lower than the room’s initial temperature, the room will get warmer.

 

I think answering the question is more fun if you answer the specific question of how much warmer the room gets, assuming a typical room volume and refrigerator power. For a 1000 W refrigerator in a perfectly insulated 25 m3 room, I found the answer surprising.

 

What result does everybody else get?

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:Exclamati: DrDick, your post constitutes rude and offensive behavior, which violates our site rules. Please don’t be rude and offensive!

 

 

As you say in your YouTube video’s, Integza, I say, assuming the refrigerator is a typical kind, has power, and is set to maintain a temperature lower than the room’s initial temperature, the room will get warmer.

 

I think answering the question is more fun if you answer the specific question of how much warmer the room gets, assuming a typical room volume and refrigerator power. For a 1000 W refrigerator in a perfectly insulated 25 m3 room, I found the answer surprising.

 

What result does everybody else get?

Hi CraigD :D

 

Thanks for your advice ... in the future i will try to make more practical examples in which i will calculate the parameters.

 

It would be fun to calculate if you are into engineering or physics already, the thing is i like to make videos accessible to anyone ... sometimes inserting math only scare  common curious.

 

When you say a 1000 W refrigerator do you mean a refrigerator that transfer 1000 Joules per second of heat or a refrigerator that produces 1000 Joules of work per second and a portion of this power is converted to heat  ?

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When you say a 1000 W refrigerator do you mean a refrigerator that transfer 1000 Joules per second of heat or a refrigerator that produces 1000 Joules of work per second and a portion of this power is converted to heat ?

Yes to both, because, assuming that the room is perfectly insulated not just against heat transfer, but against any other sort of energy transmission (ie it’s soundproof and windowless), the 2nd law of thermodynamics assures us that all of the work performed by the refrigerator is ultimately, irreversibly transformed into heat.

 

This principle takes the complexity out of "perfectly insulated room" problems. If it were better known among SciFi writers, along with a modicum of understanding of radiation laws, there’d be a lot less bad science in popular fiction. I bristle everytime I read or watch some story about folk in broken down spaceships struggling to avoid freezing, when in reality a single human being produces enough enough heat to keep it above freezing. The most serious heat problem in a large manned spacecraft is overheating in the event of failure of its cooling systems. The former happened on Apollo 13, the latter is worry on the ISS.

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  • 1 month later...

A pointless exercise if the room is insulated such that there is no heat gain or loss from the exterior, and we are only talking about inside the room.  The temperature will rise as the refrigerator uses electricity trying to reach a point of equilibrium.  It is doubtful that it will ever reach the set point of the refrigerator thermostat, as more heat is generated as the refrigerator tries to cool down to the set point.  Ultimately the room will get warmer and warmer until it collapses into a giant black hole (in terms of energy efficiency)(and mental capacity).

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