Hence, the liquid flows from B to D and the level of the liquid in the capillary falls.The impact velocity or kinetic energy of raindrops is an important factor when studying processes such as splash erosion and crusting. Hence, the hydrostatic pressure at the same levels at B and D are not equal, P B > P D. The pressure at A is the atmospheric pressure H and at D, P D \(\simeq\) H = P A. The pressure at B (P B) is greater than that at A (P A). Points C and D are just above and below the free liquid surface outside. Points A and B are just above and below the convex meniscus. (2) For a non-wetting liquid, there is capillary depression and the liquid meniscus in the capillary tube is convex, as shown in above figure.Ĭonsider again four points A, B, C and D when the meniscus in the capillary tube is at the same level as the free surface of the liquid. The excess pressure outside presses the liquid up the capillary until the pressures at B and D (at the same horizontal level) equalize, i.e., P B becomes equal to P D. The pressure on the concave side of a meniscus is always greater than that on the convex side, so that The pressure is the same on both sides of the free surface of a liquid, so that Let P A, P B, P C and P D be the pressures at points A, B, C and D, respectively. (1) When a capillary tube is partially immersed in a wetting liquid, there is capillary rise and the liquid meniscus inside the tube is concave, as shown in below figure.Ĭonsider four points A, B, C, D, of which point A is just above the concave meniscus inside the capillary and point B is just below it. As the volume of the liquid remains constant, volume of the drop = volume of n droplets Proof : Let n droplets each of radius r coalesce to form a single drop of radius R. The resulting decrease in surface energy is released into the environment as heat. This is because, the volume of the liquid remaining the same, the surface area of the resulting single drop is less than the combined surface area of the smaller drops. When two drops of a liquid are brought in contact, the cohesive forces between their molecules coalesces the drops into a single larger drop. Why two or more mercury drops form a single drop when brought in contact with each other?Ī spherical shape has the minimum surface area- to-volume ratio of all geometric forms. In most cases, all liquids are incompressible. Thus, its density has a constant value throughout the fluid. Therefore, for noticeably large h, laboratory manometer uses a low density liquid.Īn incompressible fluid is one which does not undergo change in volume for a large range of pressures. That is, p should be small for h to be large. For a given pressure p, the product hp is constant. Iv) Why is a low density liquid used as a manometric liquid in a physics laboratory?Īn open tube manometer measures the gauge pressure, p - p 0 = hpg, where p 0 is the pressure being measured, p 0 is the atmospheric pressure, h is the difference in height between the manometric liquid of density p in the two arms. Iii) What is the basis of the Bernoulli’s principle? The work done in blowing the soap bubble is W = surface tension × increase in surface area = T × 2 × 4πr 2 = 8πr 2T ∴ The increase in surface area = 2 × 4πr 2. The final surface area of soap bubble = 2 × 4πr 2 The initial surface area of soap bubble = 0 Let T be the surface tension of a soap solution. Ii) How much amount of work is done in forming a soap bubble of radius r? I) Why is the surface tension of paints and lubricating oils kept low?įor better wettability (surface coverage), the surface tension and angle of contact of paints and lubricating oils must below. V) In Bernoulli’s theorem, which of the following is conserved? Then the ratio of their terminal velocities is Iv) Two hail stones with radii in the ratio of 1:4 fall from a great height through the atmosphere. Iii) The energy stored in a soap bubble of diameter 6 cm and T = 0.04 N/m is nearly The ratio of heights through which the liquid will rise in the tubes is Ii) Two capillary tubes of radii 0.3 cm and 0.6 cm are dipped in the same liquid. What is the maximum pressure the piston would have to bear? The area of cross-section of piston carrying I) A hydraulic lift is designed to lift heavy objects of a maximum mass of 2000 kg. Maharashtra State Board 12th Physics Solutions Chapter 2 Mechanical Properties of Fluids Balbharti Maharashtra State Board 12th Physics Textbook Solutions Chapter 2 Mechanical Properties of Fluids Textbook Exercise Questions and Answers.
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