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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