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. 2 T $\left\lbrack \frac{1}{r_{1}}–\frac{1}{r_{2}} \right\rbrack$
• B. 2T $\left( \frac{1}{r_{1}} + \frac{1}{r_{2}} \right)$
• C. T $\left\lbrack \frac{1}{r_{1}}–\frac{1}{r_{2}} \right\rbrack$
• D. T $\left\lbrack \frac{1}{r_{1}} + \frac{1}{r_{2}} \right\rbrack$

Answer 1

Answer: (A)

2 T $\left\lbrack \frac{1}{r_{1}}–\frac{1}{r_{2}} \right\rbrack$

Answer 2

P₃ – P₂ =$\frac{2T}{r_{1}}$, P₂­ – P₁ = $\frac{2T}{r_{2}}$ Add both equations