Quiz - Physics - Volume/Pressure

[Angelo Farina]

Argument could be made for either a or c. But, since a tank fill is typically measured by its pressure and not volume. While, the balloon would be measured by a noticeable change in its shape (volume change). The most correct answer is c.

This depends also on the material of which the balloon is fabricated. If it is made with just a thin bladder of rubber, then the pressure inside it will increase modestly, and instead the volume will expand a lot.
If instead the balloon is, say, a basket balloon, or a water-polo balloon, these are made of a composite structure including high tensile resistance fibers (Dakron, fiberglass, Kevlar or even carbon fibers). When filled, they already contain air at 4-5 bars, hence their volume has already almost maximized.
When heated, they will behave exactly as the cylinder: a significant increment of pressure, a modest increment of volume...

 

[BlueTrin]

...

Having to interpolate the stupidity of the committee who created the question in order to guess the correct answer is BS.

I almost checked off A) because it was correct. Then I thought, no this is a PADI question, you had better read the other answers. Then I had to interpolate to get the answer that a PADI committee member would think was correct.

cheers,
m²v2

I almost chose A too before to realise that this is not likely to be what the person who wrote the question was looking for in a scuba exam.

Then once I read the other answers: it was clear that the person who wrote the question wanted us to answer c.

Also like @markmud said I think most of us know that metal expand under heat even if you don’t know the formula/coefficient and that’s enough to just answer a if you are too lazy to read all the answers.

I still enjoy the questions regardless, thanks @Pedro Burrito

 

[Ukmc]

I agree with @Angelo Farina . The volume of the tank will increase, although it would take a fine instrument to measure it. C is the better answer, however.

 

[Ukmc]

And yes, @Pedro Burrito i have not thanked you yet, but every day I look forward to your quizzes and the discussions that follow. Thank you for doing it!

 

[AfterDark]

Charles's law (also known as the law of volumes) is an experimental gas law that describes how gases tend to expand when heated. A modern statement of Charles's law is:

When the pressure on a sample of a dry gas is held constant, the Kelvin temperature and the volume will be in direct proportion.[1]

This relationship of direct proportion can be written as:

V ∝ T {\displaystyle V\propto T}

So this means:

V T = k , o r V = k T {\displaystyle {\frac {V}{T}}=k,\quad or\quad V=kT}

where:
V is the volume of the gas,

T is the temperature of the gas (measured in kelvins),

and k is a non-zero constant.

This law describes how a gas expands as the temperature increases; conversely, a decrease in temperature will lead to a decrease in volume. For comparing the same substance under two different sets of conditions, the law can be written as:

V 1 T 1 = V 2 T 2 or V 2 V 1 = T 2 T 1 or V 1 T 2 = V 2 T 1 . {\displaystyle {\frac {V_{1}}{T_{1}}}={\frac {V_{2}}{T_{2}}}\qquad {\text{or}}\qquad {\frac {V_{2}}{V_{1}}}={\frac {T_{2}}{T_{1}}}\qquad {\text{or}}\qquad V_{1}T_{2}=V_{2}T_{1}.}

The equation shows that, as absolute temperature increases, the volume of the gas also increases in proportion.

 

[wetb4igetinthewater]

What blows my mind is how you can take a large block of metal, heat it up significantly and it will be slightly heavier. The idea that energy has mass....

 

[saxman242]

What blows my mind is how you can take a large block of metal, heat it up significantly and it will be slightly heavier. The idea that energy has mass....

Or is mass just a way to measure energy!

I do appreciate that early in this thread there was a post about basic physics being a bit much for the basic scuba section and now it's turned into relativistic physics...

 

[wetb4igetinthewater]

Or is mass just a way to measure energy!

AAAARGH!!!! Stop it!

 

[Steve_C]

That a metal expands with heat is true for most metals. However, that does not immediately mean that the volume of the tank increases. It could expand both inward and outward without further information. However, I do not think that is what happens. I remember a rather obscene (in the mind of a class of 19 year old males) but physically correct demonstration in a physics class where a metal rod would not fit through a metal disk but once the disk was heated the rod slid through the hole easily.

 

[saxman242]

However, that does not immediately mean that the volume of the tank increases. It could expand both inward and outward without further information.

It does, actually. When a cylinder expands, the ID and the OD increase. It doesn't close in on itself.

When it gets hot, all of the atoms more further apart from each other. If you think of the atoms on the interior wall, the only way they can move further apart is for the interior diameter to increase. If it decreased, they'd all be getting shoved closer to each other.