Sound is Chapter 5 taken from the JKBOSE textbook of Science for students of Class 8th. In the previous post, I provided you with Questions and Answers for Chapter 4 Reproduction in Animals. This post is about the Sound Chapter 5 Class 8 Question Answers. Before we move on to solutions you must have your basics clear. So, let me begin by giving you a brief overview of what you have studied in this chapter.
Sound Chapter 5 Class 8 Question Answers
Overview of Chapter
- SOUND IS PRODUCED BY A VIBRATING BODY.
- SOUND IS PRODUCED BY HUMANS.
- SOUND NEEDS A MEDIUM FOR PROPAGATION.
- WE HEAR THROUGH OUR EARS.
- AMPLITUDE, TIME PERIOD AND FREQUENCY OF A VIBRATION.
- LOUDNESS AND PITCH.
- AUDIBLE AND INAUDIBLE SOUNDS.
- NOISE AND MUSIC.
- NOISE POLLUTION.
- MEASURES TO LIMIT NOISE POLLUTION.
SOUND IS PRODUCED BY A VIBRATING BODY: A sound is a form of energy which help us to communicate with one another. It is produced by the vibration of an object. Vibration means to and fro or the back-and-forth motion of an object. When we touch the ringing bell, our hand feels vibration.
SOUND IS PRODUCED BY HUMANS: In human beings, sound is produced in the voice box or larynx by the vibration of vocal cords. The vocal cords have a narrow slit between them. When air is passed through this slit, the vocal cords start vibrating and it produces sound.
SOUND NEEDS A MEDIUM FOR PROPAGATION: The path through which sound travels is called medium. Sound needs a medium to travel. Sound travels fastest through solids and slowest through gases. It cannot travel in a vacuum. So, medium like air, iron rods, wires etc. is mandatory for the transmission of sound.
WE HEAR THROUGH OUR EARS: We hear the sounds of different objects with help of our ears. Sound vibrations which enter our ear through the ear canal vibrate the eardrum. The vibrating of the eardrum sends the signal to the inner ear and from there, an electrical impulse is sent to the auditory nerve which goes to the brain and we hear the sensation of sound.
AMPLITUDE, TIME PERIOD AND FREQUENCY OF A VIBRATION: Amplitude and frequency are two important properties of sound. Amplitude refers to the maximum displacement of a vibrating object from its mean position. The time period is the time taken by a vibrating body to complete one vibration. Frequency is the number of oscillations a vibrating body produces in one second.
LOUDNESS AND PITCH: Loudness, Pitch and Quality are important characteristics of sound. The quality of sound which depends upon its amplitude is called loudness. On the other hand, the quality of sound which depends upon the frequency of vibration is termed the pitch of the sound.
AUDIBLE AND INAUDIBLE SOUNDS: The sounds which are detected by human ears are called audible sounds while the sounds which are not detected by human ears are termed inaudible sounds. The sounds of frequencies ranging from 20 – 20,000 Hz are audible to the human ear. The sounds lesser than 20 Hz are called infrasonic sounds while sounds having frequencies greater than 20,000 Hz are called ultrasonic sounds.
NOISE AND MUSIC: The presence of excessive and unwanted sound in our environment is called noise. The sound which pleasant to hear and has a soothing effect is termed as music. Music can become noise if it becomes too loud and irritating.
NOISE POLLUTION: The presence of excessive unwanted sounds in the environment is termed noise pollution. It leads to several health hazards like lack of sleep, anxiety, hypertension, irritation and headache etc.
MEASURES TO LIMIT NOISE POLLUTION: Several measures which can limit noise pollution are controlling noise are using silencing devices in transport vehicles, machines and home appliances. Minimal use of automobile horns. Plantation of more trees. The setting of industries away from residential areas etc.
Sound Chapter 5 Class 8th Questions
Choose the correct answer.
1. Sound can travel through
a. Gases only
b. Solids only
c. Liquids only
d. Solids, liquids and gases
Ans. d) 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
Ans. A man.
- In the following statements, tick T against those which are true and F against those which are false:
- Sound cannot travel in a vacuum. (T)
- The number of oscillations per second of a vibrating body is called its time period. (F)
- If the amplitude of the sound is large, the sound is feeble. (F)
- For human ears, the audible range is 20 Hz to 20,000 Hz. (T)
- The lower the frequency of the vibration, the higher is the pitch. (F)
- The unwanted and unpleasant sound is termed as music. (F)
- The noise pollution may cause partial hearing impairment. (T)
- Fill in the blanks with suitable words.
- Time taken by an object to complete one oscillation is called the time period.
- Loudness is determined by the amplitude of the vibration.
- The unit of frequency is Hertz (Hz).
- An unwanted sound is called noise.
- The shrillness of sounds is determined by the frequency of the sound.
- A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
- 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?
- Identify the part which vibrates to produce sound in the following instruments:
- a) Dholak b) Sitar c) Flute
|a) Dholak||The stretched membrane of Dholak.|
|b) String||Stretched strings of Sitar.|
|c) Flute||Air Column in the Flute.|
8. What is the difference between noise and music? Can music become noise sometimes?
|1. Noise is an unpleasant sound.||1. Music is a pleasant sound.|
|2. It has an irritating effect.||2. It has a soothing effect.|
|3. It causes noise pollution.||3. It does not cause noise pollution.|
|4. It causes health-related problems.||4. It does not cause any health issues.|
|5. No special instruments are needed.||5. Special instruments are needed.|
- List the sources of noise pollution in your surroundings.
Ans. The various sources of noise pollution in our surroundings are:
- Sounds of vehicle’s engine and horns.
- The noise of kitchen appliances like mixers and grinders etc.
- The explosion of crackers during festivals and occasions.
- Increased volume of T.V, tape recorders and radios etc.
- Use of loudspeakers in public rallies.
- Explain in what way noise pollution is harmful to human beings.
Ans. Noise pollution leads to a lack of sleep, hypertension, anxiety, irritation and headache and many other health-related issues. If a person is continuously exposed to the loud noise it may lead to temporary or permanent deafness.
- 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.
Ans. I would suggest that they should buy a house which is three lanes away from the roadside. This is because buying a house on the roadside means we have to bear a lot of noise from vehicles on the road which has a serious effect on our health. So, to avoid this I would suggest them to buy a house which is three lanes away from the road.
- Sketch the larynx and explain its function in your own words.
Ans. The larynx is a part of the throat, which is used to produce sound. It is also named a voice box in humans. It is located at the upper end of the windpipe in the throat. It is like a hard bump which seems to move while we swallow.
The voice box has two vocal cords stretched across it in such a way that it leaves a narrow slit between them for the passage of air.
When we speak, vocal cords stretch which leaves a narrow slit between them. When air is forced through this narrow slit, the vocal cords vibrate which produces sound. The muscles attached to vocal cords are responsible for their contraction and relaxation. The length of vocal cords in men is about 20mm, in the case of women, it is about 15 mm while children have very short vocal cords.
- 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?
Ans. It is because the speed of light is more than the speed of sound. So, the lightning is seen first and the sound of thunder is heard later on.
That’s all about Sound Chapter 5 Class 8 Question Answers. Hope you found it helpful. Do share your views about this post in the comment section below.