A thin flat circular disc of radius 4.5 cm is placed gently over the surface of water. If surface tension of water is 0.07 N m^-1 , then the excess fo - Physics MCQ NEET (UG) 2024 2026 | ExamTest.live

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A thin flat circular disc of radius 4.5 cm is placed gently over the surface of water. If surface tension of water is 0.07 N m^{- 1}, then the excess force required to take it away from the surface is:

Solution & Step-by-step Explanation

The excess force F required to lift the disc is equal to the force due to surface tension acting along the circumference.For a disc, there is only one interface (the edge), so the length is 2 π R . F = T \times 2 π R Given: T = 0.07 N m^{- 1} R = 4.5 cm = 0.045 m $ F = 0.07 \times 2 \times 3.14 \times 0.045 $ F = 0.14 \times 0.1413 = 0.019782 N F \approx 19.8 \times 1 0^{- 3} N = 19.8 mN

Try it yourself before checking the explanation above.

A thin flat circular disc of radius 4.5 cm is placed gently over the surface of water. If surface tension of water is 0.07 N m^{- 1}, then the excess force required to take it away from the surface is:

19.8 mN

198 N

1.98 mN

99 N

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