Physics.

[Parsa44]

I got this physics question in a multichoice paper and i got the wrong answer

Water is heated in a metal water tank, some thermal enegry is lost though the metal walls into the surroundings

Th air in contact with the outside metal walls:

A contracts and falls due to decreased density

B contracts and falls due to increased density

C expands and rises due to decreased density

D expands and rises due to increased density


What answer did you get and why?

 

[Smith6612]

The answer I'm going to state is C: Expands and rises due to decreased density. When air is heated, it will obviously rise and the air itself is less dense, making it lighter in a sense. Cold air is more dense, and will sink and contract. Think about water for example. Water is a lot thicker when it's colder, and the colder water is often on the bottom of a large mass of water as well. The way I'm taking this problem though, is the heated material on the inside of the metal can, and on the outside of the can, the can is giving off heat and it is combining in with the air, so it is heating up the air OUTSIDE of the can.

 

[Soki]

The answer is B.
What did you choose?

 

[stpvoice]

C-when any gas is heated, the particles are given more energy, causing them to vibrate more freely, decreasing the desity, as the gaps between atoms are larger. This air then rises above the surrounding col air because gases of different densities are immicible.

 

[vardor]

The guys bellow are right, the answere is C

 

[zen-r]

Without doubt C - didn't need a 2nd glance (BUT see my last point, below).

Air & other matter expands when heated due to increased oscillations within the particles causing them to move further apart. Since its mass remains the same, it is now less dense than the surrounding colder air. Denser matter falls in relation to less dense matter, due to gravity (not because they are "immicible"). Example of hot air rising - hot air balloons.

The only thing is, the question didn't state where the experiment took place. If it was in zero gravity conditions, such as outer space, the warm air would still expand & become less dense, but now wouldn't rise. This would require an option (E) Expand & do nothing.

So, the person who wrote the multichoice paper : FAIL :spank:

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[Teensweb]

The answer is B.
What did you choose?

thas complete'ly pointless as when a gas is heated its density decreases due to the energy gained.
Lol how can people mess up with elementary physics?