NCERT Exemplar Solutions Class 8 Science Solutions Chapter 13 Sound

# NCERT Exemplar Solutions Class 8 Science Solutions Chapter 13 Sound

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## NCERT Exemplar Solutions Class 8 Science Solutions Chapter 13 Sound

### Multiple-choice Questions

1. A list of mediums is given below.

(i) wood

(ii) water

(iii) air

(iv) vacuum

In which of these mediums can sound travel?

(a) i & ii only

(b) i, ii & iii only

(c) iii & iv only

(d) ii, iii & iv only

Answer – (b) i, ii & iii only

Sound needs a medium to propagate, but in a vacuum, there is no medium to transmit sound waves, so sound cannot travel through them.

1. The loudness of a sound depends on:

(a) its amplitude.

(b) its frequency.

(c) its time period.

(d) its speed.

Answer – (a) its amplitude.

The amplitude of a sound wave directly affects its loudness. A large amplitude results in a loud sound, while a small amplitude produces a softer sound.

1. Which of the following statements is correct?

(i) Sound is produced by vibrations.

(ii) Sound requires a medium for propagation.

(iii) Light and sound both require a medium for propagation.

(iv) Sound travels slower than light.

(a) i & ii only

(b) i, ii & iii only

(c) ii, iii & iv only

(d) i, ii & iv only

Answer is (d) i, ii & iv only

Statement iii) is incorrect as light and sound are distinct entities with different properties and behaviors..

1. An object is vibrating at 50 hertz. What is its time period?

(a) 0.02 s

(b) 2 s

(c) 0.2 s

(d) 20.0 s

Answer is (a) 0.02 s

Explanation:

If an object is vibrating at 50 hertz

50 = 1/T

T = 1/50

T = 0.02s

Its time period will be 0.02 sec

1. In order to reduce the loudness of a sound, we have to

(a) decrease its frequency of vibration of the sound.

(b) increase its frequency of vibration of the sound.

(c) decrease its amplitude of vibration of the sound.

(d) increase its amplitude of vibration of the sound.

Answer – (c) decrease its amplitude of vibration of the sound.

The loudness of sound is directly linked to its amplitude. Therefore, reducing the amplitude results in a decrease in the sound’s loudness.

1. The loudness of sound is measured in units of

(a) Decibel (dB)

(b) Hertz (Hz)

(c) Metre (m)

(d) Metre/Second (m/s)

Answer – (a) Decibel (dB)

1. The loudness of sound is determined by the

(a) amplitude of vibration

(b) the ratio of amplitude and frequency of vibration

(c) frequency of vibration

(d) product of amplitude and frequency of vibration

Answer – (a) amplitude of vibration

The loudness of sound waves increases with the amplitude. When the amplitude is high, the sound is louder, while a low amplitude results in a weaker sound.

1. 1 hertz is equal to

(a) 1 vibration per minute

(b) 10 vibrations per minute

(c) 60 vibrations per minute

(d) 600 vibrations per minute

Answer – (c) 60 vibrations per minute

Explanation:

1Hz= 1 vibration/second

1 minute=60 seconds hence 1 hertz = 60 vibrations /minute

1. Pitch of sound is determined by its

(a) frequency

(b) amplitude

(c) speed

(d) loudness

Answer – (a) frequency

1. Ultrasound has a frequency of vibration

(a) between 20 and 20,000 Hz

(b) below 20 Hz

(c) above 20,000 Hz

(d) between 500 and 10,000 Hz

Answer – (c) above 20,000 Hz

### Very Short Answer Questions

1. Lightning can be seen as the moment it occurs. Paheli observes lightning in her area. She hears the sound 5 s after she observed lightning. How far is she from the place where lightning occurs? (speed of sound = 330 m/s).

Distance=330ms x 5s

=1650m

1. Does any part of our body vibrate when we speak? Name the part.

Answer – Indeed, during speech, the vibrating component is known as the vocal cords. Positioned beneath the throat, they generate vibrations essential for speaking.

1. Boojho saw a cracker burst at night at a distance from his house. He heard the sound of the cracker a little later after seeing the cracker burst. Give the reason for the delay in hearing the sound.

Light travels faster than sound, resulting in the light from a cracker reaching an observer before the sound of the cracker. The speed of light in air is approximately 3 x 10^8 m/s, while the speed of sound in air is around 330 m/s.

1. When we hear a sound, does any part of our body vibrate? Name the part.

Answer – Absolutely, the eardrum vibrates and transmits these vibrations to the inner ear when we perceive sound.

1. Name two musical instruments which produce sound by vibrating strings?

Answer – Sitar and Veena

### Short Answer Questions

1. A simple pendulum makes 10 oscillations in 20 seconds. What is the time period and frequency of its oscillation?

Time period: 2 s

frequency : 0.5 oscillations/sec

Explanation:

A pendulum makes 10 oscillations in 20 seconds.

So it makes 1 oscillation in

20/10

sec = 2sec

Time period=2 sec

Frequency=

1/t

=

1/2

= 0.5 Hz

1. We have learnt that vibration is necessary for producing sound. Explain why the sound produced by every vibrating body cannot be heard by us?

Answer – The frequency range of vibrations differs for each vibrating object. We can hear sounds within the frequency range of 20 Hz to 20,000 Hz, which means that not all vibrations from every object are audible to us.

1. Suppose a stick is struck against a frying pan in a vacuum. Will the frying pan vibrate? Will we be able to hear the sound? Explain.

Answer – The frying pan will indeed vibrate, but we won’t hear the sound of this vibration since sound cannot propagate in a vacuum.

1. Two astronauts are floating close to each other in space. Can they talk to each other without using any special device? Give reasons.

Answer – In the vacuum of space, there is no medium for sound waves to propagate, rendering sound unable to travel. Without a medium like air, sound cannot be heard naturally without specialized equipment.

1. List three sources of noise pollution in your locality.

Answer – Industrial sirens, Vehicle honking and bursting crackers.

### Long Answer Questions

1. We have a stringed musical instrument. The string is plucked in the middle first with a force of greater magnitude and then with a force of smaller magnitude. In which case would the instrument produce a louder sound?

Answer – A string stretched with greater force produces a louder sound due to the increased amplitude. Loudness is directly linked to amplitude, so the greater the amplitude, the louder the sound.

1. How is the sound produced and how is it transmitted and heard by us?

Sound is generated when an object begins to vibrate, initiating a ripple effect. These vibrations propagate through the surrounding environment via particles until they reach their destination, our ears. Upon entering the ear, the vibrations journey through a canal to the eardrum, a taut membrane at its end. The eardrum transmits these vibrations to the inner ear, eventually reaching the brain where we perceive the sounds.

1. An alarm bell is kept inside a vessel as shown in Fig. 13.1. A person standing close to it can distinctly hear the sound of the alarm. Now if the air inside the vessel is removed completely how will the loudness of alarm get affected for the same person?

In the beginning, the individual can differentiate between sounds transmitted through air and water. However, once the air is entirely removed from the bottle, the sound will travel through the water and not reach the person. Consequently, the individual will no longer hear the sound that originally traveled through the air.

1. The town hall building is situated close to Boojho’s house. There is a clock on the top of the town hall building which rings the bell every hour. Boojho has noticed that the sound of the clock appears to be much clearer at night. Explain.

Answer – When sound begins, speed, pitch, and loudness are all set in motion by vibrations. Throughout the day, numerous vibrations surround us, leading to a reduction in the amplitude of these vibrations. Conversely, at night, the absence of such disturbances enhances sound clarity.

1. Suggest three measures to limit noise pollution in your locality.

1. i) Trees must be planted along the roads and around the buildings.
2. ii) Use of horns should be minimised.

iii) Silencers must be installed in transport vehicles and industrial machines.

### Important Topics Covered in NCERT Exemplar Solutions for Class 8 Science Chapter 13 Sound

1. Sound is generated by objects in motion
2. Human-generated sounds
3. A medium is required for sound to travel
4. Perception of sound through the auditory system
5. Characteristics of vibration: Amplitude, Frequency, and Time Period
6. Distinguishing between audible and inaudible sounds
7. Differentiating noise from music
8. Impact of noise pollution

### NCERT Exemplar Solutions for Class 8 Science Chapter 13: Key Features

NCERT’s recommendations Infinity Learn Class 8 Science Chapter 13 provides students with appropriate instruction. The Sound Class 8 NCERT Exemplar Solutions provide very detailed answers to questions from the NCERT books. Its sole purpose is to make the subject more understandable for students.

• Before taking the tests, students can review the Class 8 Science chapter Sound solutions.
• The Class 8 Science Topic 13 answer helps students have a better knowledge of the chapter and offers them more information.
• Our well-experienced specialists have created NCERT Exemplar Solutions for Class 8 Science Chapter 13 to help you quickly clear all of your difficulties.
• The NCERT Exemplar Solutions for Class 8 Science chapter sound helps you understand how to precisely answer the problems.
• The NCERT solution for Class 8 Science Chapter 13 will assist you in understanding the chapter’s principles and concepts.

For accessing the latest NCERT Solutions, NCERT Exemplar, notes, sample papers, and previous years’ question papers for Classes 6 to 12, students are encouraged to visit the Infinity Learn website. They can find comprehensive assistance for their annual exams. Furthermore, students can enhance their studies by downloading the engaging Infinity Learn App, which offers interactive videos.

## Class 8 Science Chapter 13 Sound FAQs

### Is Infinity Learn providing Solutions for Class 8 Science Chapter 13?

Yes, the Infinity Learn website comes with accurate and detailed solutions for all questions provided in the NCERT Textbook. Infinity Learn brings you NCERT Exemplar Solutions for Class 8 Science, made by our subject matter experts for a smooth and easy understanding of concepts. These solutions come with detailed step-by-step explanations of problems given in the NCERT Textbook. The NCERT Exemplar Solutions of this chapter can be downloaded in the form of a PDF and it can be used as a quick revision tool.