Physics - Fluid Question with Solution | TestHub

Volume of the water drop, $V=0.01{\mathrm{cm}}^3$
Area of the film, $A=10{\mathrm{cm}}^2$
Surface tension, $T=70\text{ dyne/cm}$

Let the thickness of the water film be $t$. The volume of the film is given by:
$V=A\times t\Rightarrow t=\frac{V}{A}$

The pressure difference across the free surface of the water film is $\Delta P=\frac{2T}{t}$.
The normal force required to separate the glass plates is:
$F=\Delta P\times A=\frac{2AT}{t}$

Substituting $t=\frac{V}{A}$ into the force equation:
$F=\frac{2A^{2}T}{V}$

Substituting the given values:
$F=\frac{2\times (10{)}^2\times 70}{0.01}$
$F=\frac{14000}{0.01}=14\times 10^5\text{ dyne}$

Since $1\text{ N}=10^5\text{ dyne}$, we get:
$F=14\text{ N}$

Answer: 14 N