Topic: Fluid Mechanics
If the surface tension of water-air interface is 0.073 N/m, the gauge pressure inside a rain drop of 1.6 mm diameter is
- A. 182 Pa
- B. 0.182 Pa
- C. 91 Pa
- D. 0.091 Pa
Answer: A. 182 Pa
Explanation: Gauge pressure inside a spherical droplet is given by $\Delta P = \frac{4\sigma}{d}$.
Given $\sigma = 0.073~N/m$ and $d = 1.6~mm = 1.6 \times 10^{-3}~m$.
$\Delta P = \frac{4 \times 0.073}{1.6 \times 10^{-3}} = \frac{0.292}{0.0016} = 182.5~Pa \approx 182~Pa$.