Question

Find the excess pressure on one side of a soap film of surface tension T over that on the other side r₁ and r₂ are radii of two surfaces.

• A. (a) $2T\left\lbrack \frac{1}{r_{1}} - \frac{1}{r_{2}} \right\rbrack$
• A. (b) $2T\left( \frac{1}{r_{1}} + \frac{1}{r_{2}} \right)$
• A. (c) $T\left\lbrack \frac{1}{r_{1}} - \frac{1}{r_{2}} \right\rbrack$
• A. (d) $T\left\lbrack \frac{1}{r_{1}} + \frac{1}{r_{2}} \right\rbrack$

Answer 1

(a)

P₃ – P₂ = $\frac{2T}{r_{1}}$…………… (i)

P₂ – P₁ = $\frac{2T}{r_{2}}$…………. (ii)

Adding (i) and (ii) P₃ – P₁ = 2T$\left\lbrack \frac{1}{r_{1}} - \frac{1}{r_{2}} \right\rbrack$