NCERT Class 9 Science Solutions: Chapter 12 – Sound Part 2

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Q 1 Image Showing Wavelength And Amplitude.

Q 1 Image Showing Wavelength and Amplitude

Question 1:

Q. What are wavelength, frequency, time period and amplitude of a sound wave?


Wavelength: The distance between two consecutive compressions or two consecutive rarefactions is known as the wavelength. Its SI unit is metre (m).

Frequency: The number of complete oscillations per second is known as the frequency of a sound wave. It is measured in hertz (Hz).

Amplitude: The maximum height reached by the crest or through of a sound wave is called its amplitude.

Question 2:

Q. How are the wavelength and frequency of a sound wave related to its speed?


Speed, wavelength, and frequency of a sound wave are related by the following equation:

Speed Wavelength Frequency

Question 3:

Q. Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.


Frequency of the sound wave,

Speed of the sound wave,

For a sound wave,

Speed Wavelength Frequency

Hence, the wavelength of the sound wave is 2 m.

Question 4:

Q. A person is listening to a tone of 500 Hz sitting at a distance of 450 m from the source of the sound. What is the time interval between successive compressions from the source?


The time interval between two successive compressions is equal to the time period of the wave. This time period is reciprocal of the frequency of the wave and it given by the relation:

Question 1:

Q. Distinguish between loudness and intensity of sound.


Intensity of a sound wave is defined as the amount of sound energy passing through a unit area per second. Loudness is a measure of the response of the ear to the sound. The loudness of a sound is defined by its amplitude. The amplitude of a sound decides its intensity, which in turn is perceived by the ear as loudness.

Q 1 Image Showing Loudness V/S Intensity.

Q 1 Image Showing Loudness V/S Intensity

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