Class 8 Sound NCERT Solutions of Science

NCERT Solutions Class 8 Science Chapter 13 Sound focuses on teaching the basic principles and theories of sound to the students. Learners must solve all the questions given in the NCERT textbook to strengthen their grip on the chapter. The NCERT Solutions for Class 8 Sound are provided below by SimplyAcad to assist you in solving these exercise problems. Students can use the answers given to understand difficult topics and revise them regularly to perform better in exams.

 

 

Access the NCERT Solutions Class 8 Science Chapter 13 Sound

1. Choose the correct answer.

Sound can travel through

(a) gases only

(b) solids only

(c) liquids only

(d) solids, liquids, and gases

The answer is (d) solids, liquids, and gases

Explanation:

Sound needs a medium to pass through. Sound travels via a medium made up of solids, liquids, and gases.

2. Voice of which of the following is likely to have a minimum frequency?

(a) Baby girl

(b) Baby boy

(c) A man

(d) A woman

The answer is (c) A man

Explanation:

A man’s voice is lower pitched than the sounds of a baby girl, baby boy, and lady. The man’s voice is the least frequent among others because of his low pitch, which is directly related to sound frequency.

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

(a) Sound cannot travel in a vacuum. (T/F)

(b) The number of oscillations per second of a vibrating object is called its period. (T/F)

(c) If the amplitude of the vibration is large, the 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 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) True: sound can only travel through a medium.

b) False: The frequency of a vibrating object is defined as the number of vibrations per second. A time period is the length of time needed to finish one oscillation.

c) False: The loudness of sound is directly proportional to the square of the vibration’s amplitude. When the vibration amplitude is high, the sound is loud. The amplitude of a weak sound is minimal.

d) True: Human ears are not capable of hearing sounds at all frequencies. Human ears can detect frequencies within the range of 20 Hz to 20,000 Hz. Human ears cannot detect sounds that are outside of these ranges.

e) False: Since pitch is proportionate to frequency, a sound’s pitch increases with increasing frequency. It vibrates at a high frequency for high-pitched sounds and a low frequency for low-pitched ones.

f) False: Music is a melodic, aesthetically beautiful sound that is enjoyable to listen to. Unpleasant sounds are called noises.

g) It’s true that noises are undesired and unpleasant sounds that, when heard repeatedly over an extended length of time, temporarily impair hearing.

4. Fill in the blanks with suitable words.

(a) The 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.

(a) The time taken by an object to complete one oscillation is called the 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.

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

The number of oscillations per second of the vibrating body is known as the frequency of oscillation.

Frequency = Total number of oscillations

Total time taken

= 50/5

= 10 Hz

The period is the time taken to complete one oscillation. It is also the inverse of frequency.

Time period = 1/Oscillating frequency

= 1/10

= 0.1 s

∴ frequency = 10 Hz

Time period = 0.1 s

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 period of the vibration?

The period is defined as the time taken to complete one oscillation. It is also the inverse of frequency.

Time period = 1

Oscillation frequency

Oscillation frequency = 500 Hz

The time period of the vibration = 1/500 = 0.002 s

7. Identify the part that vibrates to produce sound in the following instruments.

(a) Dholak

(b) Sitar

(c) Flute

a) Dholak: This instrument has a stretched membrane for a head. These stretched strings have vibrations built into them. Dholak makes a sound when the head is lightly whacked because these vibrations cause sound to be produced.

b) The sitar is an instrument of music. Part of it is stretched strings. When the string is plucked while being played, vibrations are created. The sitar makes sound as a result of these vibrations.

c) Flute: This is an instrument made of holes. The pipe is hollow. Blowing air over the pipe’s mouth causes the air within to vibrate, creating a pleasing sound.

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

A pleasing sound is what is meant to be heard. It is enjoyable to listen to the sounds of violins, pianos, and flutes.

Unpleasant sounds are known as noises.

The following sounds are unpleasant to hear:

(a) Horn noises from trucks and buses.

(b) A generator of electricity sounds.

(c) The sound of gunfire.

(d) Sounds of a jackhammer

Certainly, there are instances when loud music also produces noise.

9. List sources of noise pollution in your surroundings.

The following is a list of sources of noise pollution in our area:

Car and bus horns

(a) Loudspeakers and firecrackers

(b) Transistors and televisions with loud loudness

(d) Home mixers

e) Industrial sirens

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

Several health issues are associated with noise pollution. They are as follows:

(a) Stress

(b) Headache

(c) Hearing loss

(d) Insomnia

(e) Hypertension

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.

Purchasing a home three lanes from the roadside is preferable since the noise level will be lower than on the main road. Vehicles may be the source of the noises; the noise strength diminishes with increasing distance from the source to the listener. Therefore, purchasing a property that is three lanes away from the roadside is preferable.

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

Upon swallowing, the larynx contracts. Within the larynx are two vocal cords. There is a tiny opening that allows air to flow between them. When we talk, the lungs force air into the gap, which causes the vocal cord to vibrate and produce sound.