Question

Question 5 a. Explain why liquids in a container have a meniscus. Include a discussion of all relevant forces in your answer and give examples of different forms of meniscus. [4 marks] b. i. 50 cm3 of water flows through a pipe of radius 1 cm every second. If the pressure gradient is maintained what diameter pipe is required to double the flow rate? [1 mark] ii. What is the average flow speed in each case in b(i) above? [2 marks] iii. What is the pressure gradient in the pipe? Assume water has a viscosity of 1.0x10-3 Pa s) [2 marks] iv. The original pipe branches into 5 smaller pipes of 3 mm diameter. What is the flow speed through one of the smaller pipes? [2 marks] c. A bubble of air is observed to have a diameter of 2 cm when at a depth of 1.5 m in a swimming pool. What is the total pressure of air inside the bubble? The surface tension of water is 0.073 N m-1 and the density of water is 1000 kg m-3 . [2 marks] d. Explain the differences between the terms Elastic Limit, Compressive Limit, Tensile Strength and Compressive Strength. [3 marks] e. Explain the process of cavitation and give an example of its occurrence. [4 marks]

Answer 1

(a)

Meniscus is the upward or downward curve at the surface of a liquid in a container . A meniscus occurs because of surface tension. It may be either concave or convex

                                            

A concave meniscus occurs when the particles of the liquid are more strongly attracted to the container (adhesion) than to each other (cohesion), causing the liquid to climb the walls of the container. This occurs between water and glass. Water-based fluids like sap, honey, and milk also have a concave meniscus in glass or other wettable containers.

A convex meniscus occurs when the particles in the liquid have a stronger attraction to each other than to the material of the container. Convex menisci occur, for example, between mercury and glass in barometers and thermometers.