Question

A soap bubble is blown to a diameter of 7 cm. 36960 erg of work is done in blowing it further. If surface tension of soap solution is 40 dyne/cm then the new radius is ______ cm. Take : \(\left(π=\frac{22}{7}\right)\).

Answer 1

Correct answer is : 7

\(\omega=\Delta \mathrm{U}=\mathrm{S} \Delta \mathrm{A}\)

\(36960\ \mathrm{erg}=\frac{40 \text { dyne }}{\mathrm{cm}} 8 \pi\left[(\mathrm{r})^{2}-\left(\frac{7}{2}\right)^{2}\right] \mathrm{cm}^{2}\)

\(\mathrm{r}=7 \mathrm{~cm}\)