Poiseuille’s method is used to determine the coefficient of viscosity where liquid flows through the capillary tube at different pressures. Viscosity is estimated in terms of coefficient of viscosity. It is analogous to friction between solid surfaces, except that it comes into play only when the fluid flows. This is due to the property of the liquid called viscosity by virtue of which the liquid opposes the relative motion between its different layers. flow more freely than honey, glycerin, oil etc. Some liquids like petrol, alcohol, water etc. M l h C D T I F O To sink To tap A B Q Scale The volume collected depends on the pressure difference at the two ends of the capillary tube. By opening Q, water starts flowing through the capillary and comes out of the tube and collected in the measuring cylinder. The pinch cock Q is used to maintain a pressure difference at the two ends of the capillary tube AB. By opening the pinch cock Q, the level of water in the manometer on the B side of capillary goes down to level D. By lowering or raising the constant level tank, the pressure in the manometer can be altered. There is an excess flow tube F which helps in maintaining the water level constant. Water enters the tank from a water tap through inlet tube I and flows into the capillary tube constantly through outlet tube O. The bore of the capillary should be narrow and uniformly spherical. The capillary must be clean and free from dust or grease. The capillary tube must be placed horizontally to avoid flow of water under the effect of gravity. Poiseuille’s apparatus shown in Figure 1 consists of a capillary tube AB placed horizontally on a bench. COEFFICIENT OF VISCOSITY Introduction Some liquids like petrol, alcohol, water etc.
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