l) A scuba diver at a depth of60 m and surrounding temperature of 5 C releases a
ID: 1571485 • Letter: L
Question
l) A scuba diver at a depth of60 m and surrounding temperature of 5 C releases an air bubble of 10 cm3 a) Calculate the number of moles of the gas bubble. The pressure P at a given depth of water d is given by pgd P where p is the density of water, 1 g/cm' and g is the acceleration due to gravity b) Calculate the volume of that air when it reaches the surface, which has a temperature of 25 C.c) The buoyancy force of a given bubble is the difference in weight between the material that the bubble displaces and the bubble itself. Given this fact, calculate the buoyancy force of the bubble when it is released and compare this to the buoyancy force of the bubble at the surface. d) Does a bubble have more buoyancy at the surface or at depth? What is the main reason for this? e) Sketch a P-V diagram of the bubble and label the start (point 1) and end (point 2) of its trip. Use the diagram to estimate the work done by the bubble on its surroundings during its trip to the surface. Assume the path is a straight line The work done is the area under the line. g) Using the fact that AE nRAT for a diatomic gas, int calculate the change in internal energy of the bubble as it rises to the surface. h) Use the answers to parts (f and (g) and the first law of thermodynamics to calculate the heat added to the bubble from the surrounding water. Does this result mean that the bubble cools the water off or heats it up?Explanation / Answer
a) Here, PV = nRT
=> (1.013 * 105 + 1000 * 9.8 * 60) * 10 * 10-6 = n * 8.314 * 278.15
=> n = 2.98 milli moles
moles of gas bubble = 2.98 milli moles
b) volume of air at surface = 2.98 * 10-3 * 8.314 * 298.15/(1.013 * 105)
= 72.9 cm3
c) At 60 m depth
buyoancy force = 10 * 10-6 * 991.8 * 9.8
= 97.2 mN
At surface
buyoancy force = 72.9 * 10-6 * 991.8 * 9.8
= 0.714 mN
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