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Physics · PYQ NEET UG 2024
हिन्दीA thin flat circular disc of radius 4.5 cm is placed gently over the surface of water. If surface tension of water is \( 0.07 \text{ N m}^{-1} \), then the excess force required to take it away from the surface is:
Correct answer · Option 3
19.8 mN
Explanation
The surface tension force acts along the perimeter of the disc: \( F = T \cdot (2\pi r) = 0.07 \times 2 \times 3.1416 \times (4.5 \times 10^{-2}) = 0.01979 \text{ N} \approx 19.8 \text{ mN} \).
