|
Elements
|
- A sound wave in graphic form represents how density and pressure change when the sound wave moves in the medium.
- Compressions are the regions where particles are crowded together and represented by the upper portion of the curve.
- Thus, compressions are regions where density as well as pressure is high.
- Rarefactions are the regions of low pressure where particles are spread apart and are represented by the valley, that is, the lower portion of the curve..
- The distance between two consecutive compressions (C) or two consecutive rarefactions (R) is called the wavelength.
- The wavelength is usually represented by λ (Greek letter lambda).
- Its SI unit is metre (m).
- Frequency: The number of the compressions or rarefactions that cross per unit time indicate the frequency of the sound wave.
- It is usually represented by ν (Greek letter, nu).
- Its SI unit is hertz (symbol, Hz).
- Time Period: The time taken by two consecutive compressions or rarefactions to cross a fixed point is called the time period of the wave.
- It is represented by the symbol T.
- Its SI unit is second (s).
- Frequency and time period are related as follows: = 1 v T
 [Soft sound has small amplitude and louder sound has large amplitude]
- Pitch: How our brain interprets the frequency of an emitted sound is called its pitch.
- The faster the vibration of the source, the higher is the frequency and the higher is the pitch.
- A high pitch sound corresponds to a greater number of compressions and rarefactions passing a fixed point per unit time.
- Amplitude: Objects of different sizes and conditions vibrate at different frequencies to produce sounds of different pitch.
- The magnitude of the maximum disturbance in the medium on either side of the mean value is called the amplitude of the wave.
- It is usually represented by the letter A.
- For sound its unit will be that of density or pressure.
- The loudness or softness of a sound is determined basically by its amplitude.
- The amplitude of the sound wave depends upon the force with which an object is made to vibrate.
- A sound wave spreads out from its source. As it moves away from the source its amplitude as well as its loudness decreases.
- Louder sound can travel a larger distance as it is associated with higher energy.
- The quality or timber of sound is that characteristic which enables us to distinguish one sound from another having the same pitch and loudness.
- The sound which is more pleasant is said to be of a rich quality. A sound of a single frequency is called a tone.
- The sound which is produced due to a mixture of several frequencies is called a note and is pleasant to listen to.
- Noise is unpleasant to the ear whereas music is pleasant to hear and is of rich quality.
- The speed of sound is defined as the distance at which a point on a wave, such as a compression or a rarefaction, travels per unit time.
- We know, speed, v = distance / time = λ/T.
Here λ is the wavelength of the sound wave.
- It is the distance travelled by the sound wave in one time period (T) of the wave.
- Thus,
v = λ ν (1/T = v)
or v = λ ν
That is, speed = wavelength × frequency.
- The speed of sound remains almost the same for all frequencies in a given medium under the same physical conditions.
- The amount of sound energy passing each second through the unit area is called the intensity of sound.
- We sometimes use the terms “loudness” and “intensity” interchangeably, but they are not the same.
- Loudness is a measure of the response of the ear to the sound.
|
|
Speed of Sound in Different Media: Medium Properties and Temperature Impact
|
- Sound propagates through a medium at a finite speed.
- The sound of a thunder is heard a little later than the flash of light is seen.
- Hence, sound travels at a speed which is much less than the speed of light.
- The speed of sound depends on the properties of the medium through which it travels.
- The speed of sound in a medium depends on the temperature of the medium.
- The speed of sound decreases when we go from solid to gaseous state.
- In any medium as we increase the temperature, the speed of sound increases.
- Example: The speed of sound in air is 331 m s–1 at 0ºC and 344 m s–1 at 22 ºC.
|
[Speed of sound in different media at 25 degree celsius]