Question

What is the force required to separate two glass plates of area $3\times {10}^{-2}{m}^2$ with a film of water of thickness $0.07mm$ between them?
(Surface tension of water$=7\times {10}^{-2}N/m)$

• A. $50N$
• B. $60N$
• C. $20N$
• D. $80N$

Answer 1

The correct option is A $50N$

F=$\frac{2T{A}^2}{V}$

T=surface tension

A=area

V=volume=thickness $\times$ area

F=$\frac{2\times 7\times {10}^{-2}\times 3\times {10}^{-2}\times 3\times {10}^{-2}}{3\times {10}^{-2}\times 0.07\times {10}^{-3}}$ =60N