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A straight thread 5.0 cm long lies on a water surface. The surface tension of water is 0.076 N/m. Find the force exerted by the surface film on the thread along one of its sides.
- 1.9 mN
- 2.7 mN
- 3.4 mN
- 3.8 mN
Correct answer: 3.8 mN
Solution
The surface film pulls along the line of contact with force F = T * L. With T = 0.076 N/m and L = 0.05 m, F = 0.076 * 0.05 = 0.0038 N = 3.8 mN for one side.
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