Udit Gupta Ex-VMC Physics Faculty
WELCOME TO THE 2ND LESSON IN WAVES. The sub-topics include: thermo-d, Factors affecting the velocity of sound. Visit: unacademy.com/plus to register for SPECIAL CLASSES. Sound wave, Newton's formula, Laplace correction, Relating KTG &x
SOUND WAVE Velocity of Sound: The velocity of sound in a medium of elasticity E and density p is given by, E is maximum for solids than liquids and gases. Hence, v is maximum in solids than in liquids and gases. For solids, E-Y Young's modulus. For fluid, E = B-Bulk modulus.
NEWTON'S FORMULA Newton assumed that when sound propagates through air. Temperature remains constant (i.e., the process is isothermal). So, velocity of sound in gas is given by: Where P is the pressure of the gas and p is density of gas. At NTP. P 1.0 x 105 Nm-2 and p 1.3kqm-3 1.01 x 105 1.3 The experimental value of 279m/Sin air le 332m/* nt NTP Vair
LAPLACE CORRECTION Laplace assumed that the propagation of sound in air is an adiabatic process not isothermal. Velocity of sound in a gas is given by: Vair - YP where, y-cr_ 1.41 Cv 1.01x105 x1.41 1.3 Thus, sound waves propagate Vair - 331.3 m/s through gases adiabsatiy
RELATING KTG AND THERMODYNAMICS From KTG & thermodynamics, P RT Vair- 3RT 1 ims Hence, velocity of sound in a gas is of order of rms velocity of gas molecules.
FACTORS AFFECTING THE VELOCITY OF SOUND In a gas: v VT. So, with increase in temperature, velocity of sound also increases. Temperature Pressure Relative Humidity vair Change in pressure has no effect on velocity of sound in a gas, as long as temperature remains constant; because, The velocity of sound in air is not affected by amplitude, frequency, phase, loudness, pitch or quality. -= constant. When humidity increases, there is an increase in the relative number of water molecules and hence a decrease in the molar mass (avg. molecular weight), and the velocity of sound increases.
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A Mechanical Engineer from NIT Allahabad here to help learners with physics. Also a Star ⭐ educator.