# When is hotter in the room?

• B
Assuming there is a notebook big and hot enough to change the temperature in a room, when is hotter in that room?
a) when the thermal paste on the CPU is old and thus the temperature of the notebook gets higher.
b) when the thermal paste has been recently changed and the temperature on the processor runs lower.

Thanks.

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BvU
Homework Helper
2019 Award
Hello Ombilic,

Is this homework ?
And: what are your thoughts on this ? (This is PF culture...)

(at first I thought you had a paper notebook on fire or something )

phinds
Gold Member
2019 Award
What do you think and why?

No, It's not a homework. I had an argument with a colleague and since then we asked 4 other persons and all when with answer a.
However I think the answer is b. Considering the same amount of heat is produced in the same situations, I tend to go for b, because more of the same quantity of heat goes in the room and thus it gets hotter. I'm pretty sure my answer is the correct one, still it boggles me so many can't see this simple math. Unless I'm wrong all along, in which case.. fml I don't want live anymore after I stood up for it so strong.

phinds
Gold Member
2019 Award
I agree that "b" works in the short term since distribution of heat to the room at computer startup is quicker than in "a" but do you really think that it matters in the long run? If so, why?

Ombilic
It makes no difference in the long run as long as this notebook is capable of reaching any temperature without shutting itself down.

The point that i wanted to prove is that there is no way in which situation b grants a higher temperature than situation a. Is it right?

russ_watters
Mentor
For most ways to spin this, both answers are wrong. Conservation of energy demands that all of the heat generated be dissipated into the room.

This is true even if you count the extra heat carried by the computer, since the once you turn the computer off, the heat is dissipated into the room. And if you leave the laptop on forever, you asymptotically approach the steady state.

Ombilic
Khashishi
Agree with above, but if you add assumptions, the results will change.
If you assume that the CPU slows down when it gets hot (due to Intel's technology to prevent overheating), then it will generate less heat when it's hot.
The efficiency of the CPU probably depends on temperature. For many materials, the resistance increases at higher temperature, meaning there's a positive feedback, and you generate more heat for the same amount of processing. I don't know enough about CPUs to know if this is the case.

russ_watters
phinds
Gold Member
2019 Award
Agree with above, but if you add assumptions, the results will change.
If you assume that the CPU slows down when it gets hot (due to Intel's technology to prevent overheating), then it will generate less heat when it's hot.
The efficiency of the CPU probably depends on temperature. For many materials, the resistance increases at higher temperature, meaning there's a positive feedback, and you generate more heat for the same amount of processing. I don't know enough about CPUs to know if this is the case.
I doubt the OP was taking any of that into account. I read it as a very simple problem, not complicated by such real-world considerations.

phinds
Gold Member
2019 Award
It makes no difference in the long run as long as this notebook is capable of reaching any temperature without shutting itself down.
I assure you that is impossible. It may be that it is capable of withstanding any temperature that IT can generate (in a room with a normal temperature range) but to say that it can reach any temperature and not shut down it impossible. Try putting it in an oven on high.

Maybe I formulated the opening post wrong. The hypothesis is not a real CPU and a notebook, it's more like a heat generator. I don't want to go that deep into CPU physics as I and the others I'm having an argument with are not that good at CPU physics.

phinds
Gold Member
2019 Award
Maybe I formulated the opening post wrong. The hypothesis is not a real CPU and a notebook, it's more like a heat generator. I don't want to go that deep into CPU physics as I and the others I'm having an argument with are not that good at CPU physics.

Yes, I got my answer. Do I have to close the thread, choose an answer or anything like this?

davenn