NEETPhysicsProperties of MatterMCQ+4 / −1
A thin flat circular disc of radius is placed gently over the surface of water. If surface tension of water is , then the excess force required to take it away from the surface is
- A19.8 mN
- B198 N
- C1.98 mN
- D99 N
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Correct answer: A

$$ \begin{aligned} \& \text { Excess force }=T \times 2 \pi R \\ \& =\frac{7}{100} \times 2 \times 3.14 \times \frac{4.5}{100} \\ \& =197.82 \times 10^{-4} \\ \& =19.8 \times 10^{-3} \mathrm{~N} \\ \& =19.8 \mathrm{~mN} \end{aligned} $$
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