CBSE class 8 sound Extra Questions

(i)It is the opposite compression that reduces the density.
(ii)Two uses of echo are: -
(a)It is used to measure the depth of seas or oceans.
(b)It is used to search submarines and shipwrecks.
(iii)Flute, trumpet and saxophone.
(iv)Percussion or membrane instruments produce sound due to the vibrations occur by stretching the membrane.
(v)A melodious sound that produces a pleasing sensation is called music.

Vivek has an unpleasant voice therefore, whenever he sings the sound produced from his larynx makes everyone annoying. This unpleasant sound that irritates everyone is called noise.

Continuous producing of unpleasant sound that disturbs the environment is called noise population. Sounds of train, jet airways and drilling are examples of noise population.

We can control noise population in the following ways: -
(i)Avoid playing loud speakers in full volume.
(ii)Industrial regions should be established far away from the residential areas.
(iii)Maintaining silence at necessary places like hospitals, schools and residential areas.

Audible frequencies are the range of frequency between 20 to 20000 Hz whereas inaudible frequencies are infrasonic and ultrasonic sounds.

Given:
T= 0.2 minutes or 12 seconds
T= 1/f
f= 1/T
Therefore f= 1/12 Hz
f= 0.083 Hz

Given:
f= 100 Hz or s^-1
T= 1/f
T= 1/100 seconds
T= 0.01 seconds

Thick strings of a guitar produce a low pitch while thinner strings produce a high pitch because thinner strings vibrate faster than thicker strings.

Wind instruments produce sound because of the vibration occurs in their air column.

Human ears are the organs that enable us to hear sound. It consists of three parts: -
Outer ear: This part of ear is visible to us. It is divided into three parts: pinna, eardrum and ear canal. The pinna collects the sound waves and transfer them to the ear canal that has eardrum located at its end where these waves strike.
Middle ear: At this location, three parts are present- hammer, anvil and stirrup. The vibrations that pass through the eardrum move to these three tiny bones. Afterwards, they transfer the vibrations to the inner ear.
Inner ear: This part of ear has a long coiled-like tube called cochlea that is filled with fluid and contains many hair cells, which are highly sensitive. The vibrations move to the fluid then carried by hair cells to the brain with the help of auditory nerves. Later, the brain receives these vibrations and tries to access the memory to understand the sound.

The voice box of human beings is known as larynx. The location of the larynx in the body is the upper end of the windpipe or trachea. There are two thin membranous structures called vocal cords responsible for controlling the production of sound. They have a narrow slit where air is blown in and out. This air collides and passes through the slit vibrates and produces sound. Moreover, different pitches depend upon the thickness of the vocal cords.