As an air bubble rises from the bottom of a deep lake toward a point just below the water surface, what can be said about the air pressure inside the bubble compared to the water pressure outside it?

is greater than the pressure outside it
is less than the pressure outside it
increases as the bubble moves up
remains same as the bubble moves up

Correct answer: is greater than the pressure outside it

Solution

The excess pressure inside an air bubble in liquid is 2T/r (surface tension effect). So internal pressure is always greater than external water pressure at any depth. As the bubble rises, both pressures decrease, but the inside always exceeds the outside by 2T/r.

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