Excess Pressure and Surface Tension of Soap Bubble – Rankers Physics
Topic: Solid and Fluids
Subtopic: Surface Tension and Viscosity

Excess Pressure and Surface Tension of Soap Bubble

If the excess pressure inside a soap bubble is balanced by an oil column of height \(2\text{ mm}\), then the surface tension of soap solution will be : (\(r = 1\text{ cm}\) and density \(d = 0.8\text{ gm/cc}\))
\(4\text{ N/m}\)
\(4 \times 10^{-2}\text{ N/m}\)
\(4 \times 10^{-4}\text{ N/m}\)
4 dyne/m

Solution:

Excess pressure in a soap bubble is \(\Delta P = \frac{4T}{r}\), and the pressure of the oil column is \(h d g\). Setting them equal, \(T = \frac{h d g r}{4}\). Substituting SI values gives \(T = \frac{2 \times 10^{-3} \times 800 \times 9.8 \times 10^{-2}}{4} \approx 4 \times 10^{-2}\text{ N/m}\).

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