# Gases(Physics)

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Thread starter 10 months ago
#1
The question's screenshot is in the next post.
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Thread starter 10 months ago
#2
The picture is down below.
Please clarify why option D is correct, why not B.
I understand that air is a bad thermal conductor, but shouldn't we be heating it from down?
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10 months ago
#3
(Original post by abdullahAK)
The picture is down below.
Please clarify why option D is correct, why not B.
I understand that air is a bad thermal conductor, but shouldn't we be heating it from down?
You're logic is completely correct but you misread the Q a bit. It states "how quickly gas passes through the top and bottom", ik it doesn't specifically state it being from top to bottom etc
However, you should consider it being option D (top to bottom), because it's what comes first in respectively terms. Passes through the top and bottom. Apart from that, your logic is calm
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10 months ago
#4
Hot air creates a convection current within the box causing it to rise as it is less dense therefore allowing you to measure from the top.
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Thread starter 10 months ago
#5
Thanks to @ Hamdan and Alex.
I've got another question if you don't mind.
The screenshot is below.
C option is correct, but I was thinking about option A.
The pressure is inversely proportional to Area, So why wouldn't decreasing area work here.
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10 months ago
#6
(Original post by abdullahAK)
Thanks to @ Hamdan and Alex.
I've got another question if you don't mind.
The screenshot is below.
C option is correct, but I was thinking about option A.
The pressure is inversely proportional to Area, So why wouldn't decreasing area work here.
You’re thinking about the pressure equation where p=F/A
However that pressure is the force exerted from a solid object to a surface.
In your question it is talking about how much pressure the rock experiences
Therefore the equation you should be using is
Pressure=density of liquid x change in height x gravitational field strength
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10 months ago
#7
(Original post by abdullahAK)
The picture is down below.
Please clarify why option D is correct, why not B.
I understand that air is a bad thermal conductor, but shouldn't we be heating it from down?
I think that the point is that the question states the experiment is to investigate conductivity. If the bottom is heated then heat will be transferred from bottom to top by convection and conduction. Inverting the direction of heat flow eliminates or drastically reduces heat transfer by convection.
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Thread starter 10 months ago
#8
But the question says"Thermal conductivity of air needs to be investigated"
So, we cannot heat from above as air can only transfer heat by convection.
Could you please make it explicit to me on this @ A-Level Physics..

(Original post by A-LevelPhysicsHQ)
I think that the point is that the question states the experiment is to investigate conductivity. If the bottom is heated then heat will be transferred from bottom to top by convection and conduction. Inverting the direction of heat flow eliminates or drastically reduces heat transfer by convBut
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10 months ago
#9
(Original post by abdullahAK)
But the question says"Thermal conductivity of air needs to be investigated"
So, we cannot heat from above as air can only transfer heat by convection.
Could you please make it explicit to me on this @ A-Level Physics..
Where did you get the idea that air can only transfer heat by convection?
Heat is transfer by conduction (transfer of vibrational/rotational kinetic energy between molecules), convection(flow of molecules due to density changes) and radiation. You are now required to measure thermal conductivity so you need to heat at the top to avoid convection (I.e air moving around in the box.)
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10 months ago
#10
Air can transfer heat by conduction but very poorly. And that is the conclusion of the experiment (option D).
Edit:
If you’re interested here is air’s thermal conductivity value with some values for other materials.
Thermal conductivity (W m⁻¹ K⁻¹)
Air 0.023
Brick 1.31
Glass 0.96
Water 0.58
Last edited by A-LevelPhysicsHQ; 10 months ago
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