Question

An air bubble of radius 0.2 mm is situated just below the water surface. Calculate the gauge pressure. Surface tension of water = 7.2 x10^-2 N/m. 

Answer 1

Correct Answer: 720 N/m² 

Explaination::

Given : Radius of bubble =0.2 mm =\(2\times 10^{-4} m\)  , surface tension of water = 0.072 N/m = \(720\times 10^{-4} N/m\) 

We know that, excess pressure inside a air bubble in a liquid is given by

Where, t = surface tension of liquid r = radius of bubble

Thus, 

The gauge pressure = \(2\times 720\times 10^{-4}\over 2\times 10^{-4}\) = 720 N/m²