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but may as well be reading Swahili.Can anybody simplify the equations or put these things into laymans terms so that i can continue with my dive master exams,any help would be welcomed

Stuart

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Joined

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102 Posts

but may as well be reading Swahili.Can anybody simplify the equations or put these things into laymans terms so that i can continue with my dive master exams,any help would be welcomed

Stuart

I'd offer to help as well, but looks like you're already in much more capable hands.

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UKDivers.net - Choosing the right equipment

As an aside, is there any difference between Charles' Law and Gay-Lusac' Law?

Finally, what's the definition of Coles Law?

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102 Posts

thanks for the link i think it may clarify some of it when i get time to study the able,what i need now are some examples so i can work out how to get the correct answer

Stuart

I beleive the definition of coles law is chopped cabbage & carrot in vinegarette

Boyle's Law:

If a bottle has a volume of 2l at the surface, what will it's volume be at say 17m?

If a bottle has a volume of 3.5l at 32m, what will it's volume be at 22m?

Do each for sea water & fresh water.

Dalton's:

What's the PO2 of air at 20m?

What's the PO2 & PN2 of EANx36 at 17m?

do for both free & sea

Post ur answers, with brief calculations of how u got there (so if it's wrong we can see how u got there) and then I (or maybe someone else) will post answers/solution

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The best way to work it out is to surface it first then resink it e.g

3.5l x 3.2 ata ( plus 1 ata for the surface ) so 4.2 = 14.7 litres at the surface, then sink it to 22m

14.7 litres / (divide) 3.2 ata = 4.59 or 4.60 rounded

Partial pressure formulas are a doodle its always depth + 10 divide by 10 x percentage of gas

calculate as follows depth 20m plus 10 divide by 10 mulitply by 02 percentage in this case its 21%

so its 20 + 10 / 10 X 0.21 = 0.63

same formula again different percentage of 02 and N2 and different depth

17 + 10 / 10 X 0.36 = 0.97 PO2

17 + 10 / 10 X 0.64 = 1.72 PN2

quote "do for both free & sea"

From my recollection this is not that relevant in these examples unless its using 1.03 ata instead of 1 ata in the volume equation

Hope this helps seeing how you work out

No I was deliberately posting examples for him to work out, then post the above By answering first, the OP doesn't get the opportunity to first try to answer them himself.Not great examples from mjgreen what should have been mentioned is that in an example such as this

Not in freshwater it's not. All of your calculations above are fine for saltwater, they're wrong for freshwater.Partial pressure formulas are a doodle its always depth + 10 divide by 10 x percentage of gas

ps. (depth/10 + 1) x (percentage of gas/100) is simpler

It is. Start of DM exam booklet sets out the constants for calculations etc - weight of fresh/seawater, pressure changes per 10m in fresh/sea, & pressure changes per unit of fresh/sea are all used, and referred to in the questions (and an eagle eye may have spotted just how relevant the examples are )From my recollection this is not that relevant in these examples unless its using 1.03 ata instead of 1 ata in the volume equation

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Yes I know about the saltwater, freshwater formulas published inside the front cover of the DM exams and IDC Theory Exams and should have explained this more fully, my apologies for this.

doesn't offend me, just trying to help

Yes I know about the saltwater, freshwater formulas published inside the front cover of the DM exams and IDC Theory Exams and should have explained this more fully, my apologies for this.

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Now unless you recalibrate that gauge between a salt and fresh water dive, a reading on your gauge will be different to a tape measure. yes "10m" in salt water is slightly shallower than "10m" in fresh. HOWEVER we don't actually care about the depth, its the pressure and its effects on our body that we care about.

so if your SPG reads "10m" you're at the same pressure in salt or fresh water and the volume in your collapsable bottole will be the same.

So a question along the lines of "if you fill a collapsable container with 1 L of air at the surface and take it to 10m depth in salt and then fresh water, what is the difference in volume at 10m between salt and fresh water?" will depend on if you're using an depth gauge or a tape measure to measure depth

That may be well & true, but since he specifically asked about DM, which uses the constants given and just says 10m (thus actual depth)your SPG is a Sumersible Pressure Gauge. when you look at it underwater it is convenient to have a depth instead of a pressure. - Its easier for most people to read a gauge that says 10m rather than 2x10E5 N/m

Now unless you recalibrate that gauge between a salt and fresh water dive, a reading on your SPG will be different to a tape measure. yes "10m" in salt water is slightly shallower than "10m" in fresh. HOWEVER we don't actually care about the depth, its the pressure and its effects on our body that we care about.

so if your SPG reads "10m" you're at the same pressure in salt or fresh water and the volume in your collapsable bottole will be the same.

So a question along the lines of "if you fill a collapsable container with 1 L of air at the surface and take it to 10m depth in salt and then fresh water, what is the difference in volume at 10m between salt and fresh water?" will depend on if you're using an SPG or a tape measure to measure depth

Haha. I didn't spot that.Sumersible Pressure Gaugeto read your depth?

And there was me thinking the SPG was the thing that read your tank pressure.

Well you live and learn....

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:embarassed:what the hell was i thinking of :embarassed:Sumersible Pressure Gaugeto read your depth?

And there was me thinking the SPG was the thing that read your tank pressure.

Well you live and learn....

now i've sorted my english i think my physics still stand up

infact even a freshwater lake will give different results from a tank of distilled dionised water at STP

Do you often dive in a tank of distilled deionised water? :teeth:even a freshwater lake will give different results from a tank of distilled dionised water at STP

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Finally, what's the definition ofColes Law?

oreBk:redface:

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