SSC JE Mechanical Engineering 2014 Set 1 Paper

It is because of surface tension that pressure of a liquid increases within a bubble. The force due to surface tension at the edge is balanced by the pressure force inside the bubble. For this, $\left[2\mathit{\pi }\mathit{R}\mathit{\sigma }=\mathit{p}\mathit{\pi }{\mathit{R}}^2\right].$
So, $\mathit{p}=\frac{2\mathit{\sigma }}{\mathit{R}}.$ Thus, using this formula, pressure inside the water droplet will be
⇒ $\mathit{p}=\frac{2\mathit{\sigma }}{\mathit{R}}$ and $\mathit{R}=\frac{\mathit{d}}{2.}$
So, $\mathit{p}=\frac{2\mathit{\sigma }}{\mathit{d}∕2}=\frac{4\mathit{\sigma }}{\mathit{d}}$