Concepts

Class 9
Chapter 12 Class 9 - Sound

## Intensity

Intensity is defined as Sound power per unit area.

Intensity = Power/Area

Intensity is measured in Watt per meter square (W/m 2 )

## Loudness

Loudness is defined as a measure of the response of the ear to the sound.

Our ear may find one sound louder than other even though they may have same intensity

The loudness of a sound is directly proportional to its amplitude.

Louder sounds can travel larger distances.

Loudness is measured in decibels (db)

## Pitch of Sound

How the brain interprets the frequency of an emitted sound is called its pitch.

Pitch of a sound is directly proportional to its frequency.

Higher the pitch of the sound, more shrill it is.

## Quality or Timbre Of Sound

The quality or timber of sound is that characteristic which enables us to distinguish one sound from another even when they have same pitch and loudness.

Example - Quality of sound of 2 singers, one trained and one untrained is different

## Questions

Question 1 Page 166 (Left) - "Which wave property determines (a) loudness, (b) pitch?"

Question 2 Page 166 (Left) - Guess which sound has a higher pitch: guitar or car horn?

Question 1 Page 166 (Right Bottom) - Distinguish between loudness and intensity of sound.

NCERT Question 5 - Which characteristic of the sound helps you to identify your friend by his voice while sitting with others in a dark room?

NCERT Question 16 - What is loudness of sound? What factors does it depend on?

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