Quiz - Physics - Volume/Pressure

[Pedro Burrito]

From the PADI Dive Theory Exam.

If a balloon and a scuba tank are both filled with air and placed outdoors in direct sunlight on an extremely hot day, what will happen to each?

a. The volume of the balloon and tank will both increase.

b. The volume of the balloon will decrease and the pressure in the tank will decrease.

c. The volume of the balloon will increase and the pressure in the tank will increase.

d. The pressure in the balloon and tank will both decrease.


I will post a daily question from my exams to help newer divers and to encourage more experienced divers to interact gracefully and helpfully with the newer divers.

Reminder - this is a post in the Basic Forum and it is a green zone. Please be nice and on topic.

Thank you for your patience while we try to give people something to discuss other than Covid-19 and/or Politics. I will post the answer covered by the spoiler tag later today.

 

[scubadada]

@Pedro Burrito, One of the first things I do in the morning is look for your quiz, thanks

 

[rhwestfall]

The discussion should be interesting.

 

[Vitesse2l]

I know what happens to the pressure reading between getting my kit out of a warm car, exchanging cylinder size/contents/pressure info with my buddy and checking again in the water. There is room for discussion with the options here though, even though the voting is fairly conclusive!

 

[gamon]

I chose b and appear to be wrong. As far as the balloon volume goes, that's a no brainer.

I thought that tank gets so hot during a fill that the volume always decreases as the tank cools- and even being in the sun won't make it as hot as it gets during a fill.

Then again it might be a matter of the wording "The tank is filled with air and placed outside". Well first of all how long is it in the sun for, and are we comparing the volume of gas in the tank to what it was immediately after the fill or some time later.

Because clearly if you fill a scuba tank, put it outside for a few minutes in the sun, and then measure the pressure it will most likely be less (due to cooling following the fill), not more.

 

[Angelo Farina]

I answered c), but of course also a) is true...
Both steel and aluminium expand significantly when temperature increases.

 

[tursiops]

I chose b and appear to be wrong. As far as the balloon volume goes, that's a no brainer.

I thought that tank gets so hot during a fill that the volume always decreases as the tank cools- and even being in the sun won't make it as hot as it gets during a fill.

Then again it might be a matter of the wording "The tank is filled with air and placed outside". Well first of all how long is it in the sun for, and are we comparing the volume of gas in the tank to what it was immediately after the fill or some time later.

Because clearly if you fill a scuba tank, put it outside for a few minutes in the sun, and then measure the pressure it will most likely be less (due to cooling following the fill), not more.

There is a language ambiguity that is a problem here. What if the question were worded "full of air" rather than "filled with air"? That is, they were filled a long time ago and now are just full.

 

[Angelo Farina]

I had no doubt on the question, in this case it was clear that the examiner is asking me about the effect of HEATING both the balloon and the cylinder. Not cooling...
This was a classical quiz also at my time (1975), called "cylinders in the sun".

 

[saxman242]

While I can provide the answer the question is asking for, the pedantically correct answer is not among the choices.

So, e. the pressure and the volume of both will increase

 

[tursiops]

While I can provide the answer the question is asking for, the pedantically correct answer is not among the choices.

So, e. the pressure and the volume of both will increase

LOL. You are a slave to minor effects and decimal points. What is the major effect of the heating? Which answer is the most correct?