Question

The sufrace tension and vapour pressure of water at 20°C is 7.28 × 10^–2 Nm^–1 and 2.33 × 10³ Pa, respectively. What is the radius of the smallest spherical water droplet which can form without evaporating at 20°C?

Answer 1

According to the problem, the surface tension of water, T = 7.28 × 10^–2 Nm^–1 Vapour pressure P = 2.33 × 10³ Pa. Let r = radius of drop, which formed without evaporating.

The excess pressure (2T/r) should be greater than the vapour pressure. Then, the drop will evaporate.

Vapour pressure = Excess pressure in drop

`(2T)/r = P`

⇒ `r = (2T)/P`

⇒ `r = (2 xx 7.28 xx 10^-2)/(2.33 xx 10^3)` = 6.25 × 10^–5 m