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Mechanical Properties Of Fluids

Question
CBSEENPH11019249

An air bubble of volume 1.0 cm3 rises from the bottom of a lake 40m deep at a temperature of 12°C. To what volume does it grow when it reaches the surface, which is at a temperature of 35° C? 

Solution

At the bottom of the lake,

Volume of air bubble, V =  1.0 cm3 
Depth of lake = 40 m
Pressure at the bottom of the lake, PB = 40 m of H2O + 1 atm                                                                    =40×1000×9.8 + 1.01 ×105                                                                     = 4.93×105 Pa
Temperature, T = 12o C = 12+273 K = 285 K

At the top of the lake

Volume of air bubble = ?
Changed temperature, T' = 35o C
Pressure at the top of the lake, P= 1 atm = 1.01× 105 Pa

Volume at the top, Vt = ?

Now using the gas equation, we have

PbVbTb = PtVtTt   Vt = PbPtTtTbVb              = 4.93×1051.01 ×105×308285×1              = 5.3 cm3 

is the required volume of the air bubble at the surface.