Question

Calculate the force required to separate the glass plates of area ${10}^{-2}{m}^2$ with a film of water of$0.05mm$ thickness between them (surface tension of water $=70\times {10}^{-3}N/m)$:

• A. $28N$
• B. $112N$
• C. $5.6N$
• D. $11.2N$

Answer 1

The correct option is A $28N$

Force required to separate plates is

$F=\frac{2TA}{d}$

here,

$d=0.05mm$

$A={10}^{-2}{m}^2$

$T=70\times {10}^{-3}N/m$

By putting all these values we get,

$F=\frac{2TA}{d}$

$=\frac{2\times 70\times {10}^{-3}\times {10}^{-2}}{0.05\times {10}^{-3}}$
$=\frac{70\times 2}{5}=28N$