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)

$6.0\times 10^{-5}\,m$

Answer 2

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 $R=\frac{2 T}{P}$ $=\frac{2 \times 7.2 \times 10^{-2}}{2.4 \times 10^{3}}$ $=6.0 \times 10^{-5} m$