Question

Calculate the force required to separate the glass plate of area ${10}^{-2}{m}^2$ with a film of water $0.05$ mm thick [surface tension of water is $70\times {10}^{-3}$N/m]:-

• A. $25N$
• B. $20N$
• C. $14N$
• D. $28N$

Answer 1

The correct option is D $28N$

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

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

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

$d=$ thikness $=0.05\times {10}^{-3}m$

Hence

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