Sound Question Answers: NCERT Class 8 Science

(d) Solid, liquids and gases

Sound can travel through solid, liquid as well as through gas medium. Sound cannot travel in vacuum.

The unpleasant or unwanted sound is called as noise. Noise pollution is harmful for the human beings. Some of the health hazards produced by the noise pollution are as follows:

1. Lack of sleep
2. Hypertension
3. Anxiety
4. Headache
5. Loss of hearing etc.

I would suggest my parents to buy the house which is three lanes away from the roadsides. It will protect us from the noise pollution. The house should bought away from roads in a peaceful place which gives positive energy and keeps you calm.

Larynx is also known as the voice box. The sound is produced by the larynx. It feels like a hard bump on touch that seems to move when you swallow. This is also known as the voice box.

In the sky, lightning and thunder takes place at the same time and at the same distance from us. Lightning is seen earlier and then thunder is heard later because the speed of the light is very large in comparison to the speed of sound in air.

Speed of light = 3ooooo km/s

Speed of sound in air = 330 m/s air

(a) Baby girl

A baby girl voice is likely to have less or minimum frequency in comparison to baby boy, a man and a woman. A baby girl produced a low pitch sound.

(a) True

This statement is true because sound cannot travel in vacuum. Sound is produced by vibrations. If there, air is not present then sound cannot be produced.

(b) False

This statement is false because the number of oscillations per second of a vibrating object is called its frequency.

(c) False

This statement is false if the amplitude of vibration is large, then the sound will be sharp and having a high pitch.

(d) True

This statement is true because the range of hearing a sound is 20 Hz to 20000 Hz. Above 20,000 Hz the sound is not audible and harmful for ears.

(e) False

This statement is false because as higher is the frequency, the pitch of the sound is high.

(f) False

This statement is false because the unwanted and unpleasant sound is termed as noise pollution whereas the pleasant sound is known as music.

(g) True

This statement is true because noise pollution is harmful to the ears and it may cause partial hearing impairment. The unwanted and unpleasant sound is known as noise pollution.

(a) Time period

Time period may be defined as the time taken by an object or a body to complete the one oscillation or a cycle.

(b) Amplitude

Amplitude shows the loudness of the sound. When the amplitude of the vibration is larger, then the sound produced will be very loud. When the amplitude is small then the produced sound will be feeble.

(c) Hz

Hertz is the unit of frequency. Frequency may be defined as the number of oscillation in one second.

(d) Noise

The sound which is unpleasant and unwanted to ears known as noise whereas the sound which us pleasant to the ears is known as music.

(e) Pitch

If the frequency of the vibration is higher, then the produced sound will be shrill and it has high pitch whereas if the frequency of vibration is lower, then the sound will contain lower pitch.

Number of oscillations of pendulum = 40

Time taken = 4 second

Frequency = Number of oscillation                                                                                                                                                                                                                                   Time taken

Frequency = 40/4 = 10 Hz

Number of vibrations of mosquito wings in one second = 500

Frequency = 500 Hz

Time period =          1                                                                                                                                                                                                                                                   Frequency

= 1/500

= 0.02 second

1. Dholak: In Dholak, when stretched membrane vibrates, then it produces sound. The stretched membrane is beaten up for vibrations, then it produces sound.
2. Sitar: In Sitar, vibrations are produced by the stretched string. When the strings are pulled or we can say pushed, then production of vibrations occurs and then it produces pleasant sound.
3. Flute: In Flute, vibrations are produced by the air columns. In this, a number of holes are present, through them air produces sound. It produced a pleasant sound.

The sound which is unpleasant or unwanted to ears are known as noise whereas the sound which is pleasant to our ears known as music. Music gives us relaxation whereas noise produces so many health problems like loss of hearing, headache and many other problems.

Yes, music can become a noise sometime when the instrument like Dholak produces a very high volume of sound.

There are many sources of noise pollution around us. Some are as follows:

1. Sound produced by vehicles.
2. Sound of a loud speaker
3. Sound of bog machines in factories.
4. Sound produced at construction sites.
5. Sound produced by television at high volume.
6. Bursting of crackers produces noise pollution and air pollution too.