Class 8 Science Chapter 11 Question Answers - Sound

Q1: Discuss the importance of sound in our life.
Ans: The significance of sound in our lives is as follows:

• Sound is vital for effective communication among individuals.
• Sound helps us remain aware of events and activities even beyond our immediate focus.
• Animals rely on sound to be alert to events in their surroundings, irrespective of their attention.

Q2: How is sound produced?

Ans: Sound is produced by the vibrations of a body and is transmitted through material media in pressure waves made up of alternate condensations (forcing of the molecules of the medium together) and rarefactions (pulling of the molecules of the medium away from one another).

Q3: How does sound travel from one place to another?

Ans: Sound travels from one place to another by propagating through a medium, which can be a solid, liquid, or gas. The transmission of sound involves the generation of vibrations at the source. These vibrations create compressions and rarefactions in the medium, which are regions of higher and lower pressure respectively. As the particles of the medium collide with each other, they pass on the energy of the vibrations, allowing the sound wave to travel.

Q4: Why some sounds are louder than others?

Ans: The variation in the loudness of sounds is primarily determined by their amplitude. When a sound wave has a higher amplitude, it means that the particles in the medium are vibrating with larger excursions from their resting positions. This results in a greater displacement of air molecules, leading to more compression and rarefaction in the sound wave.

As a consequence, a sound with a larger amplitude creates more intense variations in air pressure, which our ears perceive as a louder sound. 

Q5: Explain with an activity that vibrating object produces sound.

Ans: Take metal dish pour water into it, strike its edge with a spoon, you will hear a sound, now again strike the edge of dish and look at the surface of water inside it, you will observe that vibrating dish producing sound along with wave in water. This shows that there is vibration in dish which is producing sound.

Q6: What are vibrating parts of Veena and Tabla?

Ans: Vibrating part of Veena that produces sound is stretched string and Vibrating part of Tabla that produces sound is stretched membrane.

Q7: What are vibrating parts of Flute? 

Ans: Vibrating part of Flute that produces sound is air column.

Q8: Name some musical instrument which are simply beaten or struck to produce melodious music.

Ans: Manjira, ghatam, not and kartal are some of the instruments that which are simply beaten or struck to produce melodious music.

Q9: How sound is produced from a guitar?

Ans: The string of the sitar is plucked it vibrate to produce sound, along with string other parts infact the whole instrument is forced to vibrate, and it is the sound of the vibration of the instrument that we hear.

Q10: Does any part of human body vibrate while speaking or singing a song?

Ans: Yes, while speaking or singing our voice box or larynx which is located at the upper end of the wind pipe vibrates.

Q11: Why the larynx in human body does vibrate while speaking or singing a song?

Ans: There are two vocal cords which are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for the passage of air, when the lungs force air through the slit, the vocal cords vibrate producing sound.

Q12: Explain via an activity that sound travels in liquids.

Ans: Fill a bucket with water and shake a bell under the water with one hand make sure that the bell should not touch the body of the bucket. Now place your ear gently on the water surface, you will hear the sound of the ringing bell, thus we can say that sound can travel through water.

Q13: Explain via an activity that sound travels in solids.

Ans: Take a metal rod and hold its one end to your ear, ask your friend to tap at the other end of metal rod you will hear the sound of tapping, thus this proves that sound can travels through solid.

Q14: How water animals communicate in water?

Ans: Sound can travels through liquid.Fill a bucket with water and shake a bell under the water with one hand make sure that the bell should not touch the body of the bucket. Now place your ear gently on the water surface, you will hear the sound of the ringing bell, thus we can say that sound can travel through water.

Q15: Explain the function of eardrum in human beings.

Ans: The eardrum, or tympanic membrane, is a thin, cone-shaped membrane that separates the external ear from the middle ear in humans, it is like a stretched rubber sheet, sound vibrations make the eardrum vibrate. The ear drum sends vibration to the inner ear and from there signal is send to the brain and in this way we are able to hear the sounds around us.

Q16: What is eardrum?

Ans: The eardrum, or tympanic membrane, is a thin, cone-shaped membrane that separates the external ear from the middle ear in humans, it is like a stretched rubber sheet, sound vibrations make the eardrum vibrate. The ear drum sends vibration to the inner ear and from there signal is send to the brain and in this way we are able to hear the sounds around us.

Q17: Explain the functioning of human ear.

Ans: The eardrum, or tympanic membrane, is a thin, cone-shaped membrane that separates the external ear from the middle ear in humans, it is like a stretched rubber sheet, sound vibrations make the eardrum vibrate. The ear drum sends vibration to the inner ear and from there signal is send to the brain and in this way we are able to hear the sounds around us.

Q18: Why are sound waves called mechanical waves?

Ans: Sound waves force the medium particles to vibrate, because of the interaction of the particles present in that medium.

Q19: Why there is difference in sound of a baby and an adult?

Ans: The loudness of sound depends upon the amplitude of vibration, when the amplitude of vibration is large sound produced is large and when amplitude of vibration, is low sound produced is feeble. A baby has low amplitude of vibration in their ear drum thus sound produced by baby is low in compare to adults.

Q20: Name the factor which determines shrillness or pitch of a sound?

Ans: If the frequency of vibration is higher the sound has high pitch and if the frequency of vibration is lower the sound has low pitch.

Q21: Which of the two a drum or a whistle will produce sound with higher pitch and why?

Ans: Whistle will produce sound with higher pitch.If the frequency of vibration is higher the sound has high pitch and if the frequency of vibration is lower the sound has low pitch.

Q22: Which of the two a man or a woman will produce sound with higher pitch and why?

Ans: Woman will produce sound with higher pitch.If the frequency of vibration is higher the sound has high pitch and if the frequency of vibration is lower the sound has low pitch.

Q23: Differentiate between audible and in audible sounds.

Ans: Range of sound between frequencies 20 to 20,000 Hz is called audible sound as sound between these frequencies is easily audible to human beings. But range of sound less than 20 Hz and more than 20,000 Hz is called in audible sound as sound below 20 Hz and more than 20,000 Hz is not audible to human beings.

Q24: Is there any animal that can hear sound of frequencies higher than 20000 Hz?

Ans: Yes, dog can hear sounds of frequencies higher than 20000Hz, because of this ability of dog it is being used by police for investigation purposes.

Q25: Name some equipment that works at frequencies higher than 20000 Hz.

Ans: The ultra sound equipment used for tracking and investigating many medical problems works at frequencies higher than 20000 Hz.

Q26: Define noise along with examples.

Ans: Unpleasant and undesirable sounds are called noise. Example sound produced by horns of vehicles, sound coming from construction sites, sound produced by factories machineries etc.

Q27: Explain noise pollution and its causes.

Ans: Presence of excessive or unwanted sounds in the environment is called noise pollution.

The main causes of noise pollution is the sound made by horns of vehicles, sound coming from construction sites, sound produced by factories machineries etc. in our home sound produced by television, transistor radio at high volume, airconditioner, coolers, some kitchen appliances like pressure cooker etc. contributes to noise pollution.

Q28: Your friend's parents are going to buy a house; they have been offered one nearby a factory and another 50 km away from the factory in a less crowded place. Which house you would suggest your friend's parents should buy, and why?
Ans: I will suggest to choose the house that is 50 km away from the factory in a less crowded place , because house near by the factory will have to face noise pollution because of the industrial machines and also there will be problem of air pollution there.

Q29: How noise pollution is harmful to human beings?

Ans: Noise pollution can lead to number of health related problems like

1. Hearing loss

2. Loss of sleep

3. Hypertension

4. Severe headache

5. Stress