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!

—www.raymondgreenlaw.com
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