Acoustics Flashcards
It is sometimes misinterpreted that acoustics only deals with musical instruments and design of auditoria and concert halls. But,
acoustics is a branch of physics that deals with production, transmission, reception, control, and effects of sound
Sound waves are longitudinal waves that can travel through any medium (solids, liquids, gases) with a speed that depends on
the properties of the medium.
As sound travels through a medium, the particles of the medium vibrate along the
direction of propagation of the wave
Audible waves
Audible waves These are sound waves with a frequency ranging between 20 Hz and 20,000 Hz. These are generated by vibrating bodies such as vocal cords, stretched strings etc.
Infrasonic waves
) Infrasonic waves These are sound be heard by the human ear. e.g., waves produced waves with a frequency below 20 Hz that cannot during earth quake, ocean waves, sound produced by whales, etc.
Ultrasonic waves
Ultrasonic waves - These are sound waves with a frequency greater than 20 kHz, Human ear cannot detect these waves, but certain creatures like mosquito, dogs, bats, dolphins can detect these waves. e.g., waves produced by bats.
Sound waves are longitudinal.Light waves are
transverse
In sound Wavelength ranges from
1.65 cm to 1.65 m.
In light Wavelength ranges from
4 x 10-⁷m to 7 x 10-⁷m.
When you talk about the V associated with any wave, there are two velocities, namely
particle velocity and wave velocity.
SI unit of velocity is ms-¹
Particle velocity:
The velocity with which the particles of the medium vibrate in order to transfer the energy We in the form of a wave is called particle velocity.
Wave velocity:
The velocity with which the wave travels through the medium is called wave velocity. In other words, the distance travelled by a sound wave in unit time is called the velocity of a sound wave.
V = distance/ time taken
V=nh(lamda)
Velocity of a sound wave is maximum in solids
because they are more elastic in nature than liquids and gases
In the case of solids, the elastic properties and the density of the solids affect the velocity of sound waves
Elastic property of solids is Characterized by their elastic moduli. The speed of sound is directly proportional to the square root of the elastic modulus and inversely proportional to the square root of the density
Effect of density:
The velocity of sound in a gas is inversely proportional to the square root of the density of the gas. Hence, the velocity decreases as the density of the gas increases.
V~√(1/d)
In case of gases the following factors affect the velocity of sound waves
Effect of density
Effect of temperature
Effect of relatives humidity
Effect of temperature:
The velocity of sound in a gas is directly proportional to the square root of its temperature. The velocity of sound in a gas increases with the increase in temperature. v ∝ √T. Velocity at temperature T is given by the following equation:
v₁ = (vo+0.61 T) ms¯¹
the velocity of sound changes by ______ when the temperature changes by one degree celsius.
0.61 ms-¹
Effect of relative humidity:
When humidity increases, the speed of sound increases. That is why you can hear sound from long distances clearly during rainy seasons.
Speed of sound of air at 20⁰C
343ms-¹
