Engineering
Physics
Liquid Pressure
Surface Tension and Surface Energy
Question

An air bubble of radius r is formed at a depth h below the surface of water. If P0 is the atmospheric pressure, ρ is the density of water, and T is the surface tension  of water, then the pressure inside the bubble is

Po+hρg+4Tr

Po+2Tr

P0+4Tr

Po+hρg+2Tr

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Solution

An air bubble inside water has two pressure contributions: hydrostatic pressure from depth h, and excess pressure due to surface tension. The hydrostatic pressure outside the bubble is P0 + ρgh. For an air bubble (liquid-gas interface), the excess pressure is 2T/r. Since this excess pressure acts inward, the pressure inside the bubble must be greater than outside to prevent collapse.

Therefore, the total pressure inside is: Po+ρgh+2Tr

Final answer: Po+ρgh+2Tr