Question

If the difference between pressure inside and outside of a soap bubble is $6mm$ of water and its radius is $8mm$. What is the surface tension in dynes $percm$.

• A. $117.6$
• B. $256$
• C. $378$
• D. $450$

Answer 1

The correct option is A $117.6$

The excess pressure inside a bubble is given by the expression

$P=\frac{4T}{r}$

Since, the value of this expression is given as 6mm of water

$P={10}^3\times 9.8\times 0.006=58.8N/m^2$

This should be equal to the excess pressure developed.

$58.8=\frac{4T}{0.008}$

$T=0.117N/m=117dyne/cm$

Hence option A is correct.