Question

Answer the following.

(1) Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend? Give reasons.

(2) Why can we not hear echo produced in our classroom?

(3) Why are ceilings of concert halls, cinema halls curved?

(4) Which type of waves are sound waves? State their characteristics.

(5) Explain auditory aspects of human ear.

Answer 1

(1) I will not be able to hear any sound produced by my friend because there is no atmosphere on the moon, which means that there is no material medium for sound propagation.

(2) An echo is heard when the time interval between the original sound and the reflected sound is at least 0.1 s. This means that the minimum distance between the source of sound and the wall to hear the echo should be 17.2 m. However, this type of situation is not available in our classroom so we cannot hear the echo.

(3) Ceilings of cinema and concert halls are curved so that sound after reflection (from the walls) can spread uniformly in all directions.

(4) A sound wave is a mechanical wave which is longitudinal in nature and which requires a material medium for its propagation.

Characteristics of sound waves:

Amplitude (A)

Amplitude of a wave is the maximum displacement of medium particles in either direction from their equilibrium (rest) position. Its SI unit is metre (m). The transverse equivalent of a longitudinal sound wave is shown in the figure.

MP = QC = amplitude

Loudness and Intensity

In common context, we interchange the term loudness with the term intensity. These two terms are quite different from each other.

Loudness is the measure of response of a sound by a human ear whereas intensity is the amount of energy passed per unit area per unit time.

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

ME = CG = Wavelength

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

Pitch: The highness or lowness of a sound proportional to its frequency is also called pitch. It is the shrillness of a sound.

Time period (T)

The time required to complete one full oscillation or cycle is called the time period. It is also defined as the time interval between two consecutive crests or troughs of a wave. Its SI unit is second (s).

It is the inverse of the frequency of the wave i.e.,

(5) The ear is the most important organ for a human being to hear sound. It is used to convert the sound signal of the hearing range into electrical signals that propagates to the brain through auditory nerve. The ear has three major parts:

(i) outer ear

(ii) middle ear

(iii) inner ear

The outer part, pinna, collects the sound which is carried to the ear drums through the auditory canal. The cochlea then converts the vibrations into electrical impulses which are carried by auditory nerves to the brain where the sound is heard.