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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