• # question_answer If the surface tension of water-air interface is 0.073 N/m, the gauge pressure inside a rain drop of 1 mm diameter will be: A) $0.146\,\,\text{N/}{{\text{m}}^{\text{2}}}$                B) $0.73\,\,\text{N/}{{\text{m}}^{\text{2}}}$C) $146\,\,\text{N/}{{\text{m}}^{\text{2}}}$                   D) $292\,\,\text{N/}{{\text{m}}^{\text{2}}}$

$p\,\,=\,\,\frac{4\sigma }{d}\,\,=\,\,\frac{4\,\,\times \,\,0.073}{1\,\,\times \,\,{{10}^{-\,3}}}$ $=\,\,292\,\,\text{N/}{{\text{m}}^{\text{2}}}$