plz answer Q 16,17,18
Answers
16.Newton assumed that when sound propagates through air, temperature remains constant (i.e. the process is isothermal).
So, bulk modulus of elasticity B = BT = p
(isothermal bulk modulus BT of a gas is equal to its pressure).
Therefore at NTP
p = 1.01 × 105 N/m2 and ρ = 1.3 kg/m3
= 279 m/s
The experimental value of v in air is 332 m/s at NTP. This discrepancy was removed by Laplace.
LAPLACE’S CORRECTION :
Laplace assumed that the propagation of sound in air is an adiabatic process not the isothermal.
B = Bs = γP [Adiabatic bulk modulus Bs of a gas = γP]
Where γ = Cp/Cv = 1.41 for air
Which is in agreement with the experimental value (332 m/s) thus,
17.Effect of pressure (at constant Temp)
Physical Factors Affecting of sound
Thus, velocity of sound is independent of change of pressure at given temperature.
2) Effects of Temperature:
Since the velocity of sound in gas,
Physical Factors Affecting of sound
i.e. the velocity of sound in gas or air is directly proportional to the square root of absolute temperature.
3) Effect of Density:
At constant pressure,
Velocity of sound in gas is inversely prop to sq. root of density.
4. Effect of humidity:
The of water vapor is small that of dry air i.e. presence of moisture in air reduce density of air, since the velocity of sound in gas is inversely proportional to sq. root of its density then velocity of sound in humid air is greater than that of dry air.
5. Effect of Wind:
If the air is flowing, the speed of the sound changes. If wind blow in direction of sound, velocity of sound increases and vice versa.
6. Effect of frequency wave length & amplitude:
Velocity of sound in air is independent of frequency wave length. Sound wave of different frequencies travel with the velocity in air though their wavelength in air are different the velocity is also independent of amplitude as well however if amplitude is very large, the compression and rarefaction may result in large temperature variation and this affect the velocity.
18 ITS under 17