Class 9 Science Note
Sound is the form of energy which is produced due to the vibration of molecule.
Sound wave is the mechanical wave which needs material medium to propagate.
Propagation of sound takes place through compression and rarefaction.
It shows the properties of reflection, refraction diffraction and interference.
Factors influencing the velocity of sound
Density: The velocity of sound decreases with increase in the density of the medium.
Temperature: The velocity of the sound increases with increase in temperature.
Humidity: The velocity of sound in air increases with increase in humidity.
Pressure: The velocity of sound is independent o pressure.
Direction of air flow: If the sound propagation take place in the direction of air flow then its velocity increases.
Pitch of the sound
It is the property of sound that distinguishes between the sharp of shrill sound from dull or flat. Pitch the sound depends on the frequency .Higher the frequency higher will be the pitch. Pitch is not the measurable quantity.
Intensity of sound
It is the measure of the loudness of the sound .It may be defined as the rate of flow of sound energy through the unit surface area normal to the direction of propagation. It is measured in w/m2
Factors determining the loudness of the sound:
Amplitude of the sounding body
Distance between the source and observer
Density of the medium
Surface area of the sounding body
Presence of the other sounding body
Reflection of sound
When the sound wave strike on the rigid surface a part of it is absorbed and a rest is reflected back is called reflection of sound. It follows the laws of reflection. Sound can be reflected from walls of big building, hills or row of trees.
Refraction of sound waves
Sound waves also follow the property of refraction. Sound travels in a constant speed in a uniform medium. When the medium is not uniform, it changes its speed. Because of the temperature there is no uniformity in the air medium at different layers. So, the bending of sound wave in a layer of different temperature is called refraction.
The sound which produces an unpleasant effect is called noise. It is a unwanted sound.
Effects of sound pollution
Causes the different disease like, increase in sugar level, blood pressure e.t.c
Ways to reduce the sound pollution
By using the sound absorbing materials
Shifting the noisy source away from the sources