First slide

Surface tension

Question

Work W is required to form a soap bubble of soap solution of volume V. What amount of work is required to be done to form a bubble of volume 8V?

Moderate

A

16W
B

2W
C

4W
D

8W

Solution

If T be the surface tension of soap solution and r be the radius of smother bubble then,
$\begin{array}{l} W = 2 \times 4 {πr}^{2} \times T = 8 {πr}^{2} T \\ Now \frac{4}{3} {πR}^{3} = 8 \times \frac{4}{3} {πr}^{3} \Rightarrow R = 2 r \\ ∴ W^{'} = 2 \times 4 {πR}^{2} T = 4 \times 8 {πr}^{2} T = 4 W \end{array}$

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