Question

What will be the diameter (in $\text{mm}$) of a water droplet, the pressure inside which is $0.05{\text{N/cm}}^2$ greater than the outside pressure? (Take surface tension as $0.075\text{N/m}$).

• A. $3$
• B. $0.3$
• C. $0.6$
• D. $6$

Answer 1

The correct option is C $0.6$

Given,
Excess pressure inside water droplet,
$\Delta P=0.05{\text{N/cm}}^2=0.05\times {10}^4{\text{N/m}}^2$
Surface Tension, $T=0.075\text{N/m}$
To find: diameter of water droplet, $d=?$
We know that, excess pressure inside a water droplet is given by
$\Delta P=4T/d$
$\Rightarrow d=\frac{4T}{\Delta P}$
Substituting all the values,
$d=\frac{4\times 0.075}{0.05\times {10}^4}=0.6\text{mm}$