A 5.0 cm long straight piece of thread is kept on the surface of water. Find the force with which the surface on one side of the thread pulls it Surface tension of water = 0.076 N m-1.
3.8 × 10-3 N
Given, length of thread,
Surface tension of water,
Therefore, force due to surface tension is
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The surface tension and vapour pressure of water at 20°C is 7.28×10-2 Nm-1 and 2.33×103 Pa, respectively. What is the radius of the smallest spherical water droplet which can form without evaporating at 20°C?Physics - Exemplar
Surface tension is exhibited by liquids due to force of attraction between molecules of the liquid. The surface tension decreases with increase in temperature and vanishes at boiling point. Given that the latent heat of vaporisation for water Lv = 540 k Cal kg-1, the mechanical equivalent of heat J = 4.2 J cal-1, density of water ρ w = 103 kg l –1, Avogadro’s No NA = 6.0 × 1026 k mole –1 and the molecular weight of water MA = 18 kg for 1 k mole.
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(b) show that the inter–molecular distance for water is 1/3 and find its value.
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(d) During vaporisation a molecule overcomes a force F, assumed constant, to go from an inter-molecular distance d to d′. Estimate the value of F.
(e) Calculate F/d, which is a measure of the surface tension.
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