Charles` Law - Ray Greenlaw

Charles’ Law
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
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
 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
 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
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
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.
 What happens if we fill tanks on a hot afternoon and
dive the next day on a very cold morning?
 Naui Master Scuba Diver Manual, 2010.
 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.
 Thanks for coming!

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