NCERT Solutions for Class 8 Science Chapter 13 Sound

NCERT Solutions for Class 8 Science Chapter 13 Sound are given below. Here we have provided the best and error-free answers to all the exercise questions that will strengthen your foundation in science. Solving NCERT questions will assist you in grasping the content in the Crop Production and Management chapter in a better way.

In these solutions, we have answered all the intext and exercise questions provided in NCERT class 8 science textbook. NCERT Solutions for Class 8 Science Chapter 13 Sound provided in this article are strictly based on the CBSE syllabus and curriculum. Students can easily download these solutions in PDF format for free or can read them online.

Sound Class 8 Science NCERT Solutions

Exercise Questions

Question 1: Choose the correct answer: 

Sound can travel through 

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

Answer: (d) solids, liquids and gases.

Explanation: Sound requires a medium to travel through. Solid, liquid and gas provide the medium for sound. Hence, sound can travel through solids, liquids and gases.

Question 2:  Which of the following voices is likely to have minimum frequency? 

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

Answer: (c) A man 

Explanation: Frequency of a sound is directly proportional to its pitch and inversely proportional to its amplitude. The voice of an adult man is of lower pitch and high amplitude in comparison to the voices of a baby boy, a baby girl and a woman. The voice of a baby girl has highest pitch among this group.

Question 3: 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)

Answer:

(a) True

Sound requires a medium to travel through. Since vacuum is devoid of any medium, sound cannot travel through it.

(b) False

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

(c) False

Loudness of a sound is proportional to the square of the amplitude of its vibration. When the amplitude of vibration of a sound is large, the sound is very loud. The sound is feeble for small amplitude.

(d) True

Humans cannot hear sounds of all frequencies. Humans can hear a sound whose frequency falls in the range of 20 Hz−20,000 Hz. The sound having frequency out of this range is inaudible to humans.

(e) False

The pitch of a sound is proportional to its frequency. As the frequency of vibration increases, the pitch of the sound also increases and vice-versa. A sound is said to be high pitched if its frequency of vibration is high, and is low pitched for a small frequency of vibration.

(f) False

Unwanted or unpleasant sounds are known as noise. Sounds that are melodious and pleasing to ear are known as music.

(g) True

Unwanted or unpleasant sounds are known as noise. If one is subjected to loud unpleasant sound continuously for a long time, then it may cause temporary hearing impairment.

Question 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) The shrillness of a sound is determined by the __________ of vibration.

Answer:

(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) The shrillness of a sound is determined by the frequency of vibration.

Question 5: A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.

Answer: Here no. of oscillation = 40
Time taken = 4s

Question 6:  The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration?

Question 7: Identify the part which vibrates to produce sound in the following instruments

(a) Dholak
(b) Sitar
(c) Flute

Answer:  

(a) Dholak: Dholak has stretched membranes which vibrate to produce sound.

(b) Sitar: In sitar, the stretched strings, when vibrate, they produce sound.

(c) Flute: Flute is a wind musical instrument which uses air column to produce sound.

Question 8:   What is the difference between noise and music? Can music become noise sometimes?

Answer: Music is a sound which produces a pleasing sensation while noise is an unwanted and unpleasant sound. Music is produced by nature, musical instruments etc. Noise is produced by horns of vehicles, by machines etc.

Music can become noise when we play it at very high volume or too many music are being played at the same time with unpleasant loudness.

Question 9:  List sources of noise pollution in your surroundings.

Answer: Some sources of noise pollution are as follows:

(i) Televisions and transistors running at high volumes

(ii) Loudspeakers and crackers

(iii) Horns of buses, cars and trucks

(iv) Home appliances such as mixer, desert cooler, etc.

Question 10:  Explain in what way noise pollution is harmful to humans.

Answer:  Lack of sleep, hypertension (high blood pressure), anxiety and many more health disorders may be caused by noise pollution. 
A person who is exposed to a loud sound continuously may get temporary or even permanent impairment of hearing.

Question 11:  Your parents are going to buy a house. They have been offered one on the roadside and another three lanes away from the roadside. Which house would you suggest your parents should buy? Explain your answer.

Answer: There will be more noise in the house which is along the roadside. This is because noise produced by transportation vehicles may cause trouble to the residents. The intensity of noise decreases with the distance between the source and the listener. Hence, it is better to take the house that is three lanes away from the roadside. 

Question 12: Sketch larynx and explain its function in your own words.

Answer: When we swallow something, the larynx moves.  There are two vocal cords inside the larynx. The air passes through a small gap which is present in between them. The lungs force the air into the gap when we speak and this vibrates the vocal cord, due to which sound is produced.

Question 13: 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?

Answer: Speed of sound is 330 m/s and speed of light is 300,000,000 m/s. Light travels much faster than sound that is why lightning is seen earlier and thunder is heard. 

NCERT Solutions for Class 8 Science Chapter 13 – A Brief Discussion

CBSE Class 8 Science NCERT Solutions Chapter 13 helps students to clear their doubts and to score good marks in the board exam. All the questions are solved by experts with a detailed explanation that will help students complete their assignments & homework. Having a good grasp over CBSE NCERT Solutions for Class 8 Science will further help the students in their preparation for board exams and other competitive exams such as NTSE, Olympiad, etc.