A soap bubble of radius r is connected to one side of a manometer. The difference in liquid levels is h and the manometer-liquid density is ρ. Find the surface tension T of the soap solution. Image
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Question

A soap bubble of radius r is connected to one side of a manometer. The difference in liquid levels is h and the manometer-liquid density is ρ. Find the surface tension T of the soap solution. Image

G1 Physics · Accepted Answer

Step 1: The excess pressure inside a soap bubble is ΔP = 4T/r. Step 2: The manometer gives ΔP = ρgh. Equating, 4T/r = ρgh, so T = rρgh/4. Correct answer: B.