Concepts

Class 9
Chapter 12 Class 9 - Sound

We have already learnt that Sound waves cause Compression and Rarefaction

In compression

Particles of medium (air particles) are tightly packed, hence there is more density and more pressure

In refraction,

Particles of medium (air particles) are loosely packed, hence they have less density and less pressure

## Plotting them on Graph

We get peaks and trough as follows

Note

The peak represents region of highest compression. It is called the crest.

The valley represents region of rarefaction. It is called the trough.

## What is Wavelength of Sound Wave

The distance between any two consecutive compressions or rarefactions is called wavelength.

SI unit of wavelength is metre (m)

It is denoted by lambda. (λ)

Explanation

Wavelength is the distance between

2 consecutive compressions (2 Crests)

or

2 consecutive Rarefactions (2 Troughs)

It is denoted by lamda (λ)

Its SI Unit is meter

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#### Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 13 years and a teacher from the past 17 years. He teaches Science, Economics, Accounting and English at Teachoo