a) Give an approximate range for the fluctuations in air pressure associated wit
ID: 2086909 • Letter: A
Question
a) Give an approximate range for the fluctuations in air pressure associated with sound and comment on these in the light of the assumption that sound is transmitted by weak" pressure waves. 4 marks] Calculate the Mach number of a body travelling at 300 m/s through still air at a temperature of 25 °C. Take the gas constant, R, and the ratio of specific heat capacities, x, for air as 0.2869 kJ/kg K and 1.4 respectively. b) [6 marks] c) Derive an expression for the theoretical mass discharge rate from a large reservoir of fluid through a small orifice, where the flow rate is such that variations in density are important (i.e. the fluid cannot be assumed to be incompressible). Your expression should be in terms of the fluid pressure and density in the reservoir, the pressure ratio between the reservoir and the orifice, the cross sectional area of the orifice and the ratio of specific heat capacities, y, for the fluid [15 marks]Explanation / Answer
a) Human auditory system can sense fluctuations in air pressure above and below the barometric static pressure. These are the fluctuations which are called as sound. Human Ear can detect pressure changes in the audible frequency range. Humans can hear 20 hertz to 20000 hertz of frequencies. All of these frequencies cannot be heard equally well. Frequency weighing is done which approximates frequency range 1000 to 5000 hertz.
Human ear initially detects a high pressure and compression arrives. Then it detects normal pressure in the next instant. And low pressure is finally detected. These fluctuations are detected at periodic and regular time intervals. Alternating low and high pressure waves make membrane to vibrate to and fro and sound is detected.
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