Charles’ Law
By Raymond Greenlaw
Learning Objectives
State Charles’ Law
Understand Charles’ Law
Apply Charles’ Law
Explain relevance of Charles’ Law to scuba
Jacques Charles/Joseph Louis Guy-Lussac
Ballooner and scientist
1787
Did not publish, sometimes called Charles/Guy-Lussac’s Law after Joseph Louis Guy-Lussac
Temperature Scales
State Charles’ Law
For any gas at a constant pressure, the volume of the gas is directly proportional to its absolute temperature.
State Charles’ Law
Mathematically,
V1/T1 = V2/T2, where Vi is volume and Ti is temperature in Kelvin
V/T = k, where k is a constant
Recall 0K = -273C and oK = -460F
Note, pressure remains the same
Charles’ Law Illustrated
Understand Charles’ Law
Temperature goes up volume goes up
Temperature goes down volume goes down
Rubber glove thought experiment
Gas molecules thought experiment
Balloon in the morning thought experiment
Example
2 liters of gas at 273C
1 liter of gas at oC
Since V1/T1 = V2/T2, we have 2/546 = 1/273
Note, we converted temperatures to Kelvin by adding 273 as required by Charles’ Law.
If we cool by 273C, we reduce volume by 1 liter.
If we heat by 273, we increase volume by 1 liter.
Apply Charles’ Law
Not fully (XL) BCD contains .3 liters of air on a cool morning at oC
BCD is left in a car and the temperature sores to 40C
What is the new volume of air in the BCD, assuming it is still not totally full?
Apply Charles’ Law (We assume no change in pressure.)
We know intuitively that the volume goes up.
.3/273 = x/313, so x = .34 liters
Explain Relevance of Charles’ Law to Scuba
We learned that as temperature increases volume increases.
Consider a full cylinder of air.
When heated the volume wants to increase by Charles’ Law, but in a tank there is no room for expansion, so the pressure must increase.
Extreme temperature increases could result in a tank bursting.
Do not leave full scuba tanks stored in direct sunlight or heat them.
Getting Bent
We know nitrogen dissolves in a diver’s body tissues under pressure.
Suppose a diver goes deep and a lot of nitrogen dissolves in body tissues.
As the diver surfaces, the diver is not bent.
However, exposure to intense sunlight could cause gas coming out of solution to increase in volume (temperature goes up volume increases), so the diver could get bent.
Question
What happens if we fill tanks on a hot afternoon and dive the next day on a very cold morning?
References
Naui Master Scuba Diver Manual, 2010.
answers.yahoo.com
www.thescubaguide.com
www.wikianswers.com/Q/What_is_Boyle’s_law_in_regards_to_scuba_diving
Figures borrowed from around the web, please let me know if any of the figures are not in the public domain and I will replace them.
Questions
Thanks for coming!
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