Question

The surface tension and vapour pressure of water at $30^{\circ} C$ are $7.2 \times 10^{-2} N / m$ and $2.4 \times 10^{3}$, respectively. What is the radius of the smallest droplet of water which can be formed without evaporating at $30^{\circ} C$ ?

• A. $ 1.6\times 10^{-2}\,m $
• B. $ 2.9\times 10^{-3}\,m $
• C. $ 5.6\times 10^{-4}\,m $
• D. $ 6.0\times 10^{-5}\,m $

Answer 1

Answer: (D)

The given, $T=7.2 \times 10^{-2} N / m$
$P=2.4 \times 10^{3} N / m ^{2}$
or Pa $R=?$
We know that, $P=\frac{2 T}{R}$
or $R=\frac{2 T}{P}$
$=\frac{2 \times 7.2 \times 10^{-2}}{2.4 \times 10^{3}}$
$=6.0 \times 10^{-5} m$