# Cubic expansion question

#### steve12

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

#### OlderDan

Homework Helper
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

http://en.wikipedia.org/wiki/Pressure

#### steve12

thanks for that-much appreciated!

### The Physics Forums Way

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving