Sound is produced by vibrating objects. The matter or substance through which sound is transmitted is called a medium. It can be solid, liquid or gas. Sound moves through a medium from the point of generation to the listener. When an object vibrates, it sets the particles of the medium around it vibrating.
Sound
Definitions
“Energy in the form of sound causes our ears to experience hearing.“
The creation of sound
The vibrating of items results in the production of sound.
An elastic body or medium vibrates when its constituent particles move back and forth on a regular basis around a central axis. It also goes by the name oscillation.
For example:
A guitar’s stretched strings vibrate to create sound.
A table’s membrane vibrates when it is tapped, creating sound.
The Propagation of sound
Sound propagation is the term used to describe how sound moves.
The to-and-fro motion of the medium’s particles is what causes sound to travel.
The particles in the medium vibrate when a thing does. First, the particle in contact with the vibrating object is moved out of equilibrium. Each particle that comes into contact with another gets disturbed. As a result, the disturbance is transmitted to the listener from the source.
The only thing that moves across the medium is the disruption that the vibrating body creates; the particles themselves do not.
Medium of sound
A medium is the material or thing that allows sound to be conveyed through it.
Sound waves can only travel through a medium.
Solid, liquid, or gas might be the medium.
In a vacuum, sound cannot travel.
A mechanical wave is one that needs a medium to propagate.
Wave
Energy is transported from one point to another without there being any direct contact between them, which is a phenomena or disturbance known as a wave. For instance, waves are said to be composed of heat, light, and sound.
Types of Waves
On the basis of direction of propagation, waves are categorized into two parts:
(I ) Longitudinal waves: These waves occur when medium particles vibrate in the wave’s direction of propagation. Consider a sound wave.
(ii) Transverse waves: In this kind of wave, the medium’s particles vibrate perpendicular to the wave’s path of propagation. For instance, the waves created by a stretched string.
Electromagnetic waves are a different class of wave that can travel through any medium. These waves can also pass through a vacuum. X-rays and light waves are two examples.
Compressions and Rarefactions:
The portion of a wave known as compression occurs when medium particles are closer to one another, creating a zone of high pressure and density.
The crest, or upper part, of the curve symbolise compressions.
In the rarefaction phase of the wave, particles disperse to create an area of low pressure and density.
The trough, or bottom part of the curve, represents rarefactions.
Characteristics of a sound wave
Sound waves have following characteristics:
(1) Amplitude
(2) wavelength
(3) Frequency
(4) Time period (5)Velocity
Amplitude.
The maximum displacement of each particle from its mean position is called amplitude.
It is denoted by A.
Its SI unit is metre (m). Its CGS unit is Centimeter (cm)
Wavelength
The distance between two nearest (adjacent) crests or troughs of a wave is called its wavelength.
It is denoted by the Greek letter lambda (λ).
Its SI unit is metre (m). Its CGS unit is Centimeter (cm)
Frequency
The number of vibrations per second is called frequency.
The SI unit of frequency is hertz (Hz).
The symbol of frequency is ν (nu).
Time period
The time taken to complete one vibration is called time period.
It is denoted by T.
Its SI unit is second (s).
The frequency of a wave is the reciprocal of the time period.
i.e., v = 1/T
Velocity
The distance travelled by a wave in one second is called velocity of the wave or speed of the wave.
Its S.I. unit is metres per second (m/s).
Velocity = Distance travelled/Time taken
⟹ v = λ/T , (where λ = wavelength of the wave travelled in one time time period T)
⟹ v = λv (As 1/T = v)
Thus, Velocity = Wavelength × Frequency
v = λv is called the wave equation.
Pitch and loudness of Sound
Pitch: It represents shrillness of sound.
It depends on the frequency of vibration. Higher the frequency of sound wave, the higher will be the pitch of sound and vice-versa.
Loudness: It is a measure of the sound energy reaching the ear per second.
It depends on the amplitude of the sound wave.
It is measured in decibel ‘dB‘
Music And Noise
Music: It is the sound that is pleasant to hear. For example: Sound coming out of musical instruments
Noise: It is the sound that is unpleasant to hear. For example: Sound produced by vehicles.
Tone and Note
Tone: A pure sound of single frequency is called tone.
Note: An impure sound produced by mixture of many frequencies is called a note. For example: A musical note has tones of various frequencies.
Audible Frequency
The audible range of human ear is 20 Hz and 20,000 HZ, i.e., the human ears can hear only those waves whose frequency lies between 20 Hz and 20,000 HZ.
Reflection of sound
When sound waves strike a surface, they return back into the same medium. This phenomenon is called reflection of sound.
Laws of reflection
There are two basic laws of reflection of sound:
(i) Angle of incidence is equal the angle of reflection. ( < i = < r )
(ii) The incident wave, the reflected wave and the normal all lie in the same plane.
Applications of Reflection of Sound
Many instruments work on the basis of multiple reflections of sound:
Megaphones, loudspeakers, bulb horns, and musical instruments like trumpets and shehnais, among others, are made to send sound by many reflections in a certain direction, increasing the volume of the sound as a result.
The stethoscope, which doctors use to hear the noises coming from the human body, likewise operates on the idea of numerous sound reflections. Here, many reflections allow the sound of the heartbeat to reach the ears of the doctor.
Large auditoriums and halls have sound-absorbing walls, ceilings, seats, etc. As a result, a curved sound board is positioned behind the speaker. The speaker’s voice is then subjected to several reflections to make it louder so that listeners may readily hear his discourse.