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Cubic expansion question

  1. Dec 10, 2006 #1
    1. The problem statement, all variables and given/known data
    Hi,i came across this problem in a past exam paper and i got a bit stuck on it,can anyone enlighten me please?im prob just missing something really obvious and basic....

    A spherical air bubble at the bottom of a lake,10m below the surface,has a radius of 1mm. The temperature at the bottom of the lake is 4.0degrees celsius. The bubble gets dislodged and rises slowly to the surface,where the temperature is 27degrees celsius.if the atmospheric pressure is 1030 mbar,what is the radius of the bubble just before it reaches the surface?(neglect surface tension)

    2. Relevant equations
    i really dont know....

    3. The attempt at a solution
    my first problem is that i dont know the conversion factor for millibars to an SI pressure unit,or if i even need to convert the pressure value to SI units?

    could i possibly use ratios to solve for the volume of the bigger bubble,such as the ideal gas equation: P1*V1/T1= P2*V2/T2?
    and then use the volume of a sphere formula to solve for the radius?

    although i dont think this approach is right as i would not be making use of the ten metre figure??any ideas or hints would be fantastic,as they dont give solutions at the back of the papers,just answers,which arent really that much use to me... thanks
  2. jcsd
  3. Dec 10, 2006 #2


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    Your approach is generally correct. You would be making use of the 10 meters in finding the pressure difference between the two locations. 1 bar is 10^5 Pa

  4. Dec 10, 2006 #3
    thanks for that-much appreciated!:biggrin:
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