# NCERT Solutions For Class 8 Science Chapter 13 Sound

NCERT solutions for class 8 science chapter 13 Sound: In day to day life, you hear a variety of sounds. Have you ever thought that how sounds are produced? What makes male and female voices so different from each other? You will get the know answers to these questions in solutions of NCERT class 8 science chapter 13 sound. After studying the chapter attempt NCERT exercise of science chapter 13. For better preparation CBSE NCERT solutions for class 8 science chapter 13 sound are helpful. You must have observed that when we take a steel bucket and hit it with a small hammer, vibrations are caused. These vibrations are responsible for the production of sound. Production of sound in humans is mainly due to the presence of a voice box or larynx. It is found to be present at the upper end of the windpipe. You will understand the structure of the voice box and mechanism of production of sound by voice box after studying this chapter. The solutions of NCERT helps students in solving homework problems.  The NCERT solutions for class 8 science chapter 13 sound give an explanation to 13 exercise questions.

## NCERT solutions for class 8 science chapter 13 sound exercise:

Sound can travel through

(a) gases only  (b) solids only     (c) liquids only     (d) solids, liquids and gases.

Sound can travel through solids, liquids and gases. But the sound does not travel in a vacuum

(d) is correct.

(a) Baby girl  (b) Baby boy  (c) A man  (d) A woman

Voice of a man would have the lowest frequency since it is of a lower pitch than the voice of a woman, a baby boy and a baby girl. Pitch is proportional to frequency.

(c) is correct

Q3. In the following statements, tick ‘T’ against those which are true, and ‘F’ against those which are false.

(a) Sound cannot travel in vacuum. (T/F)
(b) The number of oscillations per second of a vibrating object is called its time period. (T/F)
(c) If the amplitude of vibration is large, sound is feeble. (T/F)
(d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T/F)
(e) The lower the frequency of vibration, the higher is the pitch. (T/F)
(f) Unwanted or unpleasant sound is termed as music. (T/F)
(g) Noise pollution may cause partial hearing impairment. (T/F)

(a) T.

Sound cannot travel in a vacuum as it requires a medium to travel.

(b) F.

The number of oscillations per second of a vibrating object is called its frequency. Time period is the time taken to complete one oscillation.

(c) F.

The sound of a vibration is directly proportional to the square of the amplitude of vibration, therefore, the sound will be feeble if the amplitude of vibration is low.

(d) T.

For humans, the audible range of frequency is 20 Hz to 20,000 Hz.

(e) F.

The pitch of a sound is directly proportional to its frequency.

(f) F.

Unwanted or unpleasant sound is termed as noise.

(g) T.

Exposure to loud noise for a long period of time may cause partial hearing impairment.

4. Fill in the blanks with suitable words.

(a) Time taken by an object to complete one oscillation is called __________.
(b) Loudness is determined by the __________ of vibration.
(c) The unit of frequency is __________
(d) Unwanted sound is called __________ .
(e) Shrillness of a sound is determined by the __________ of vibration.

(a) Time taken by an object to complete one oscillation is called time period.
(b) Loudness is determined by the amplitude of vibration.
(c) The unit of frequency is Hertz.
(d) Unwanted sound is called noise.
(e) Shrillness of a sound is determined by the frequency of vibration.

Time Period is defined as the time taken to complete one oscillation.

$\\Time \ taken \ to \ complete \ 40 \ oscillations\ = 4 \ seconds\\ Time \ taken \ to \ complete \ 1 \ oscillation\ = \ \frac{4}{40}\ seconds\ = \ 0.1 \ second\\$

Frequency is defined as the number of oscillations per second.

$\\Number \ of \ oscillations \ in \ 4 \ seconds \ = \ 40 \\ Number \ of \ oscillations \ in \ 1 \ second \ = \ \frac{40}{4} \ = \ 10\\ Frequency \ = \ 10 \ Hertz.$

The time period of vibration is defined as the time taken to complete one oscillation.

$\\Time \ taken \ to \ complete \ 500 \ vibrations \ = \ 1 \ second.\\ Time \ taken \ to \ complete \ 1 \ vibration = \frac{1}{500} \ second \ = \ 0.002\ seconds.\\ Time \ period \ = \ 0.002 \ seconds.$

Time Period = 0.002 s.

(a) The stretched membrane over the body of the dholak vibrates to produce sound.

(b) The strings stretched over the body of the sitar vibrate to produce sound.

(c) The air inside the flute vibrates when air is blown into it to produce sound.

Noise is sound which is irritating and unpleasant whereas music is sound which is pleasant and soothing. Music can turn into noise at very high volume.

Sources of noise pollution in our surroundings are:

(a) Horns of vehicles on the road.

(c) Crackers.

(d) Machinery inside factories and appliances at homes.

(e) The noise produced by a large number of people.

Noise pollution can cause several health-related problems such as:

(i) Insomnia.

(ii) Anxiety and stress.

(iii) Hearing impairment

I would suggest them to buy the one three lanes away from the roadside as there will be less noise pollution caused by vehicles moving on the road.

Inside the larynx, there are two vocal cords with a gap between them and when air passes through this gap the vocal cords vibrate and as we know the sound is produced when something vibrates, therefore, this vibration of vocal cords inside the larynx produce sound.

## Q13. Lightning and thunder take place in the sky at the same time and at the same distance from us. Lightning is seen earlier and thunder is heard later. Can you explain why?

The speed of light is much faster than the speed of sound, due to this the light emitted by lightning reaches our eyes before the sound of thunder reaches our ears and we see lightning before we hear thunder.

## NCERT Solutions For Class 8 Science Chapter wise:

 NCERT solutions for class 8 science chapter 1 Crop Production And Management Solutions of NCERT class 8 science chapter 2 Microorganisms: Friend And Foe CBSE NCERT solutions for class 8 science chapter 3 Synthetic Fibres And Plastics NCERT solutions for class 8 science chapter 4 Materials: Metals And Non-Metals CBSE NCERT solutions for class 8 science chapter 5 Coal and Petroleum NCERT solutions for class 8 chapter 6 Combustion and Flame Solutions of NCERT class 8 science chapter 7 Conservation of Plants and Animals CBSE NCERT solutions for class 8 science chapter 8 Cell Structure and Functions NCERT solutions for class 8 science chapter 9 Reproduction in Animals Solutions of NCERT class 8 science chapter 10 Reaching the Age of Adolescence NCERT solutions for class 8 science chapter 11 Force and Pressure CBSE NCERT solutions for class 8 science chapter 12 Friction NCERT solutions for class 8 science chapter 13 Sound NCERT solutions for class 8 chapter 14 science Chemical Effects of Electric Current Solutions of NCERT class 8 science chapter 15 Some Natural Phenomena CBSE NCERT solutions for class 8 science chapter 16 Light Solutions of NCERT class 8 science chapter 17 Stars and The Solar System NCERT solutions for class 8 science chapter 18 Pollution of Air and Water

## NCERT solutions for class 8 science chapter 13 sound: points to remember

• Sound requires a medium to travel. This medium can be a gas, liquid or solid. Questions are discussed based on this concept in the NCERT solutions for class 8 science chapter 13 sound.
• Hearing is a process in which eardrum senses vibration and send signals to the brain.
• Larger the amplitude, the louder will be the sound. Larger the frequency more will be the pitch
• Some sounds are pleasant as that of a musical instrument and some are unpleasant as that coming from horns, some home appliances and factories, etc.
• The range of audible frequency for humans is 20 to 20000 Hz.
• Noise pollution is caused due to excessive unpleasant sounds. This can cause various health problems. Questions based on this are discussed in CBSE NCERT solutions for class 8 science chapter 13 sound.