Hello everyone welcome to Magnet Brains Today we will learn about Sound As I am talking to you, you are able to hear my sound So this is used for communication Sound helps us to communicate with each other We hear a lot of different types of sounds around us Automobile horn, musical songs We hear birds chirping These are all different types of sounds. These different sounds are produced in nature. We human beings can produce them. How do we human beings produce sound?
We have some organ which produces sound. Flute is a musical instrument that produces sound. Harmonium produces sound.
Wires produce sound. Tabla produces sound when we tap it. These are many musical instruments and we get many sounds from them.
Similarly, we will know what is there in our body that produces sound in this chapter. So, how sound is produced? We have already known many sources of sound, but how sound is produced? As you can see here, if I talk about this tabla, then if I hit the surface of the tabla with a rod or with my hand, then it sounds.
Similarly, if I hit a metal surface with a rod or a wooden stick, or if I hit a steel pot with a rod, wooden stick say my little chaotic sound reduce with a the sound cube reduce with a to get job up new stick say us metal surface my mouth of vibrations produce we the vibrating body produces sound so yeah my conclusion oh yeah he vibrating body he can't get sound reduce cut the So if we take a metal plate and strike it with a stick, we feel vibrations and the vibration produces the sound. So what is vibration? To and fro motion of an object. object. Like if I hit on any tablet, I see its membrane which is its outer most surface, it vibrates from top to bottom.
So this to and fro motion is known as a vibration and vibrating body only produces sound. So if we talk about vibration is the only cause of which sound produces. So, here you can see another example. Suppose I took a metal vessel and I tapped it with a rod on the outer surface.
So, as soon as I tapped it, Now I am telling you that the sound is produced due to vibration. How will I prove this? Very easily, you fill some water in the vessel of this tamba. up to the brim.
So when you filled the water and then you again strike it like this, then you will see waves came in the water. So what are these waves that you saw in the water? Because there are vibrations that are traveling through the water.
So for this we can prove that vibrating, vibration is necessary for production of sound. Because what are those vibrations doing? So, up here, because water is producing waves so you can understand that yes vibrating body produces sound sound is produced by vibrating body and you must have heard about this musical instrument Ek Tara so you can see its picture here if you go to market you will find this Ek Tara you get it in a very finished form, a very good instrument which is made properly, but how can we make a string at home?
This part you can see can also be made from coconut, the outer most brown color of coconut covering with it and then this thing is the strings that we have attached so this Ek Tara is a musical instrument and it can be played now again these strings which we talk about guitar, there are strings in guitar we play those strings with our hands, by doing this those strings vibrate on musical sound produce hota hai. To again we have proved that vibrating body produces sound. Again kuch aur examples mai apko de deti hu jo musical instrument hai. Yaha par aap dekh sakte hai ghatam, manjeera.
We play it like this. When we tap both the surfaces against each other, vibrations are produced in the air which we hear in the form of musical sound. So these are again two examples of musical instruments. Okay, next let's do an activity.
I'm sure you have seen this. There are many bowls in which we have filled water. And if we tap them one by one, we get a musical sound. And we call this Jaltarang.
Jal means water and Tarang means waves. So the musician taps on the outer surface of all the balls through a stick. So the sound comes and that sound Why does it come?
Of course, there is some vibration. And how will we see this vibration? As soon as the water-flag is playing, as soon as they tap on the outer surface of the bowl, they will see that there are waves in the water. And these waves are coming because of the vibration. And as soon as this vibration passes through the air through the water, this vibration is heard in the form of musical sound.
And that is known as Jaltarang. So this setup is capable of producing music. So I am sure you have observed this sometime or the other. So this is known as Jaltarang. So again if we strike all these in order, one after the other, in succession, then musical sound is produced.
So I hope this is clear to you that sound is produced by vibrating body. So this is called vibrating body. In our next video, we will learn how human beings produce sound. If you have missed our previous videos, then you can watch all the videos of class 8 science on our official site magnetbrains.com. Till then, thank you.
Hello everyone, welcome to Magnet Brains. Today we will learn about sound. This is the topic of class 8 science.
In the previous video we saw that vibrating body produces sound. And today we will learn about the vibrating part in our human body. sound produces.
Have you heard about this? If yes, then please tell us how is sound produced in human body in the comment section below. So before that I would like to give you an I would like to tell you a observation. When we touch a part of our throat, we feel that some vibration is coming.
So the vibration that is coming, is the organ that produces sound. So we call it vocal cord. And this vocal cord vibrates, that is when sound is produced in human beings.
open vocal cord and this is closed vocal cord. So now you understood which instrument is responsible for producing sound? Vocal cord. But where does this vocal cord exist?
We know that this vocal cord is on the upper part of our windpipe. So the one on the upper end of the windpipe is our vocal cord. Actually a vocal cord which has a In the middle of the voice box is the larynx. So the larynx is the voice box and what happens in the voice box? The voice produces the vocal cords.
So there are two vocal cords in the voice box and there is a narrow slit in between them through which air can pass. So when air passes through the lungs through the narrow slit, what happens is that the vocal cords start vibrating and sound is produced. So this is how sound is produced in human beings through the help of vocal cords which are present in the voice box known as larynx.
So, if I tell you how our vocal cords work, then you can see it in a similar way. You can do this at home too. Take two papers and put a gap between them, i.e. air, so that it can pass.
And then blow from there. Blow like this. So it will be that you will hear the sound. So similarly, there is an opening between our two vocal cords, there is a slit. through lungs air comes from the lungs so they vibrate and sound is produced.
Similarly when I blow from here also, what will happen is that they will vibrate and sound will be produced. As soon as the vibrations pass through the air, sound will be produced. will be produced so this is how sound is produced by our vocal cords also because vocal cords ke beech mein bhi humne padhai kya hai slit hai aur yaha pe bhi hum kya bol rahe hai ki narrow slit hona chahiye between the two papers so I hope this is clear to you Again, if I tell you to go to space, can two people talk to each other in space? No. because there is no air in space and if there is no air then how will it work?
so I am sure you must have seen that in space as we know there is no air that is why oxygen mask and everything is carried by the astronauts. And if there is no air, then sound is also not heard from each other. What is the proof of this?
That sound needs a medium to move or propagate. That means sound needs a medium to travel from here to there. So what medium is there between you and me that is giving you sound? It is air.
If I put air in this room, then sound is not heard. instead of a sound, I create a vacuum like in space, you will not be able to hear my voice. So this proves that sound needs a medium to propagate. We can do this through an activity too. For example, you took a glass and put a phone in it.
Now you told your friend to call this phone. So when your friend calls this phone, this phone vibrates. will produce sound and that sound will reach you because there is air here which will reach the sound. There is air between you and this phone.
But if you do one thing, if you put your mouth on this glass and suck all the air and create vacuum in this portion, then the sound produced by the phone will not be able to travel and will not reach you. So, if you suck the air, then the sound will not be able to travel. If sound goes to air, then it will produce vacuum and sound cannot travel in vacuum because sound needs some medium to travel.
Sound needs a medium to travel. So can that medium be only air? Can sound propagate only through gas and air?
Or can it propagate through liquid, water or a metal rod? What do you think? Please do comment in the comment section below. Can sound travel through water?
what is the answer yes or no please comment so sound needs a medium to travel this is clear here that medium is air so when air has been removed completely so what is created is vacuum and sound cannot travel through vacuum so we cannot talk to each other in space so now let's see this Let's do an activity. Take a bucket, fill it with water. Take a small bell in one hand.
So if you take a bucket or a tub filled with water and you... and place your ear on the surface of water and place your hand on the surface of water and press the bell so what do you think? Do you hear the sound of the bell? Yes, because it is proving that sound can also travel through water. So, we will not put our ears in water otherwise what will happen?
Water will enter in the ears and there will be a lot of irritation. So, what will we do? We will just put our ears on the surface of water and put the bell inside the water and ring it.
So, the sound will definitely be heard. So, what does this prove? Prove, scan, sound.
can travel through water or through liquid now again take our activity up her picker said tip yeah but up make wooden box Leah up to the straw friend behind her bow behind tap kar raha hai us wooden box ko aur yaha par aap awaaz sun rahi hai apna kaan laga ke aapko awaaz tunai deti hai ki nahi mujhe zarur batayega ki aap ne ye observe kiya ki nahi but the answer is that yes yaha par is friend ko zarur awaaz tunai deti hai jab wo wala friend waha se tap karega kyunki sound can travel through wood or metal. So you can do one more thing, you can take a pipe, there must be a pipe in your house which is a steel or metal pipe. So hold one end, give one end to your brother or sister.
and ask them to scratch the other end of the sound. You must hear the sound of scratching from the other end. You will definitely hear it. Because sound can propagate through metal.
So these are some activities. which you can prove at home that sound needs a material medium to propagate and that can be air, water or metal and solid substances. So I hope this is clear to you. So now how do we produce sound? Through our vocal cords which vibrate.
We have already read this. How do we listen to sound? You all will say through ears. So what happens in the ear that it produces sound?
How does it design? How does the sound come in our ears? Where does it travel?
Where does it go? Let's see. So this is a diagram of human ear.
So of course you know that sound comes from here. Suppose if I talk to someone, why will the sound go to their ears? Because there is air between me and them and through air, that sound is passing on.
So, just like sound So, first of all, how is the structure of your ear? See, this is a funnel. I am sure you have seen it. Make this funnel horizontal. This is the funnel.
is the shape of the ear also same? yes so this funnel is funnel shaped ear the shape of the ear is like a funnel as soon as the sound enters then first of all it will come through the canal and we call it ear canal and of course you have sometimes when you scratch your ear with your finger then wax comes out so that is deposited in the outer ear in this part this is the outer ear only this part is the part of outer ear and definitely the inner part This part is your inner ear and this middle part is your middle ear. So this middle ear part is the middle ear, this part is the inner ear and this is the outer ear. So here is the ear canal through which the voice travels. and then it will hit the ear drum.
Now what is a drum? A drum is a covering on the drum which vibrates. It is an elastic covering.
When we tap it, the covering moves. So this ear drum, as soon as the sound hits it, it is like a membrane and as soon as the sound hits it, it starts vibrating. What does the ear drum do?
The ear drum vibrates. Because that is also a... like a membrane.
So let's revise this process. The shape of our ear is like a funnel and as soon as the sound reaches the ear drum through the ear canal, then what does a thin membrane do? It vibrates.
So the ear drum vibrates. Now what will happen? Where will these vibrations go from the ear drum? These vibrations will go to the inner part of the ear. So as soon as these vibrations go to the inner part of the ear, there are some nerves.
which makes this vibration reach to the brain and then brain interprets these vibrations and then it understands what it heard. So these vibrations from the ear drum pass on to the inner ear and from there they pass on to the brain. So the signal then goes to the brain from the inner ear. So now you have understood that there are three parts of the ear, outer ear, middle ear and inner ear.
Yes. You will learn more about this in class 10th. So how do we hear?
We hear through our ears and it is because in our ears there is an ear drum which is a thin membrane which vibrates when sound reaches it. Like if I tell you that you take a pipe and you put a rubber on one side of it. stretch the ear drum and cover it.
And now if you blow on it, then what will happen? The covering of the rubber will vibrate like this. Similarly, our ear drum is there. When sound reaches it, what does it do?
It vibrates and then these vibrations pass on to the inner ear and brain and the brain interprets that message. So next we'll study about the properties of sound. So first of all is amplitude, then time period and frequency.
So as you can see, sound travels. My voice is reaching you. Because sound is propagating through the medium known as air. So now what is this? You can see these are waves.
So I want to tell you this. When I am speaking, I am also traveling in the form of these waves. So here you can see these are sound waves.
sound waves. So how does sound travel? In the form of sound waves. So we have made a wave and the distance of a wave is amplitude and if I talk about a whole wave, this wave which is starting from here, it is coming from here and from here. So this whole distance from point number 1 to point number 2, this whole distance, this whole wave is over.
So this whole distance is called the length of a wave. So basically we will call the wavelength of a wave, we will call the can define wavelength as you can see here the topmost two points the distance between them so the distance between the topmost two points is wavelength so wavelength is the distance so how will we measure it? in meters and if we talk about amplitude this is the distance like amplitude is wavelength and frequency is also a sound key property so what is frequency frequency kya hoti hai jaisa ke agar mai bolu movie jaane ki meri frequency hai four times a month yaani ki mai 4 baar ek mahine me movie jaate ho to meri frequency ho gai four times in one month similarly frequency of an oscillation kyunki hame pata hai ki oscillation ki frequency kya hogi number of oscillations in one second to per second jatni oscillations produced by those what is its frequency so if we talk about frequency I have talked about a month but generally we talk about one second how many oscillations are there in a second what will happen frequency and we have read in class 7 that frequency units are hertz which symbol is HZ so I hope amplitude wavelength frequency you have understood all these terms and we have read about time period that frequency is one upon time time period. So we have also studied the relationship between frequency and time period.
So I hope you have understood some properties of sound. In our next video we will study about noise pollution. Till then thank you. Hello everyone, welcome to Magnet Brains.
Today we will study about sound. So we have studied about sound and its properties. We have also studied how we human beings produce sound.
Through our are voice box larynx which contains vocal cords or maybe a particular hum sound through the ears because of the incoming sound or signal brain. So in today's video we will read about some properties of sound like loudness and pitch. So you must have heard about the word pitch about loudness.
Like if my pitch is high then what does it mean? If loudness is high then what does it mean? So in today's video we will see the difference between these two first. So, first of all we have to study about loudness.
So, we have a set up here. You can also buy a glass tumbler or steel glass. and you can see a metal ball through this metal ball, we have attached it with a thread and we have hit the glass slowly if we hit it slowly, then we will hear the sound and if we hit it very fast, then we will hear the sound this is loudness first the loudness was less when we hit it slowly later the loudness is more when we hit it hard the loudness is more when we hit it hard Loudness is decided by amplitude of waves.
The amplitude of sound wave is as much as loudness. And the less amplitude, the less loudness. So I hope you understood the meaning of loudness. So we simply have to read in this video that loudness is related to amplitude of sound wave.
And pitch is related to frequency of sound wave. So I hope you understood what loudness means. It means the sound is heard slowly or fast.
The amplitude of the sound wave increases. Now we will talk about pitch. Pitch depends on frequency.
Amplitude of vibration will be large. So loud sound will be produced. Frequency of vibration will be high.
So pitch will be high. So frequency determines the pitch. Like I am talking to you. So, if I talk about a bird's voice and a lion's roar, do you understand the difference?
So, the bird's voice is called high pitch and we hear that shrill voice. But if I hear the sound of a lion's roar, it is a low pitch sound. So, if we talk about this in terms of physics, low pitch means low frequency and high pitch means high frequency. and we have already studied what is frequency number of waves in 1 second, number of oscillations in 1 second so when number of oscillations will be more in 1 second then high pitch sound will be produced and number of oscillations will be very less in 1 second so that will be low pitch sound like that of a lion so I hope you have understood the difference between loudness and pitch and which property of sound wave depends on it So next let's study about the audible and inaudible sounds. So sometimes you have seen that when small children, newborn babies, they wake up at night and start crying.
So one of the reasons for that is that The reason is that they hear sounds that we adults cannot hear. Do you know why this happens? What are the sounds that they hear and we cannot hear? There are some sounds that they hear and we can't hear them and we can't hear those sounds because they are outside our range of the ear. So there is a range of our ears listening and that range is from 20 to 20,000 Hz.
So the sound that will come between 20 to 20,000 Hz, I will be able to hear that. So the sound that will be lower than 20 Hz or the sound that will be more than 20 Hz, whose frequency is more. I will not be able to hear that but sometimes babies can hear less than 20 Hz so they get scared and start crying.
So what is the range for human ear? 20 to 20,000 Hz. So those sounds which are audible to us, we should like them in between this range.
The range outside this will be inaudible for us, we will not be able to hear it. Except for the newborn babies. Next, we will talk about noise pollution. The unwanted sounds are noise.
Like the excessive horns of cars, or the loudness of loudspeakers, music. All these things, all these noises, are they required? I am talking to you now, I am teaching you, it is required. These are wanted noises. But if you don't hear the sound of someone playing the horn loudly from outside, then it is unwanted noise.
So, we call unwanted sound as noise. So, unwanted sound is known as noise and it is unpleasant to hear. As you can see here, she is closing her ears because she is hearing a lot of noise of automobile planes. So, I hope this is clear.
If I ask you, is there noise for you in musical sound? No, if you like music, you have that musical sound. If you like it, then that is not noise for you. So musical sound is pleasing to hear, but unpleasant sounds are known as noise.
Next, noise pollution. So, the excess of unwanted sounds, if we call it noise, if its extent increases, then it is called noise pollution. What will happen with noise pollution? anxiety stress as you can see here that this picture is showing you stress so hypertension anxiety lack of sleep suppose you are sleeping and someone is singing loudly on loudspeaker in your colony at 1 in the night what will happen you will face lack of sleep So this lack of sleep is due to unwanted noise.
Like if I say that crackers are blowing at night during Diwali, music is playing in loudspeaker during marriages, so all this is very unwanted and all these sounds are unwanted and cause noise pollution. And what are the results of noise pollution? Lack of sleep, hypertension and if you have a lot of noise, high sound continuously goes in your ear for a long time, then it can cause permanent or temporary deafness.
You can be deaf forever. So it is very necessary to protect yourself from noise pollution. So I hope this is clear to you. Measures to limit noise pollution.
So how to stop noise pollution? Government has made rules that loudspeakers should not be used after 11 pm. In marriages and parties, everything should be wind up. Again, excessive use of horns should be minimized by us and there should be rules to minimize it. So this is how you can control or limit noise pollution.
For example, if you are talking about extra noise coming from your car, then you have installed some silencing device. So that the noise is reduced or the noise is completely limited. So these are the factors that will help you to limit noise pollution.
So, Noisy operations should be carried away from residential area. Means the machines, if there is a lot of noise coming from the machines, then where should you install those industries and factories? Those factories should be situated there, where there should be no effect from their sound, means it should be far away from the residential area. And what can we do? We can plant trees.
Trees, do you have sound? absorb so we should increase the planting of trees and afforestation again in some buildings we have seen that curtains are kept so those curtains also absorb sound so they absorb unwanted noise and don't let it come inside so these are some measures which you can follow to control noise pollution so I hope this chapter sound is clear to you and if it is not then please please go to our official website magnetbrains.com and there you can see all the videos of this chapter because in the next video we will discuss the frequently asked questions of this chapter in which you have to participate so till then thank you hello everyone welcome to magnet brains Today we will study about sound. We will discuss all the questions of this chapter of NCRT which is important for your exams.
So we have read this chapter completely and I am sure you have understood it. And if you have not understood it then please read our chapter. official website magnetbrains.com and visit it and watch the videos and you can download notes from there from class 4th to 12th. So let's begin. Choose the correct answers.
Sound can travel through So we have learnt that sound can travel through metal or wooden box or through water and air and it is still travelling through air when I am talking to you. So the answer would be solid, liquid and gases. All three. Voice of which of these is likely to have minimum frequency?
So if I talk about frequency, the one whose pitch is low, the frequency of that will also be low. So if I talk about the pitch of which of these is low? So as compared to a baby girl, a baby boy and a woman, Man's voice is low pitched. That's why its frequency will be minimum. Because we know frequency is directly proportional to pitch.
So we know the lowest pitch is man's voice. That's why it will be the lowest frequency. That is why minimum frequency.
So I hope this is clear. Next. state which of the following is true or false sound can not travel in vacuum so we know that sound needs a medium to propagate so it cannot travel in vacuum so this is true the number of oscillations per second of a vibrating object is called as its time period. So, that is not time period but frequency.
That is why this is false and frequency is 1 upon time period. If the amplitude of a vibration is large, sound will be feeble. No, the more the amplitude, the louder the sound.
We read that loudness is directly proportional to amplitude. For human ears, the audible range is 20 to 20,000 hertz. Is this right?
Yes, we have read that it is heard in the same range. The lower the frequency of vibration, the higher is the pitch. No, we just read that frequency and pitch is directly proportional.
So this statement is false. Unwanted and unpleasant sound is termed as noise and not music. So this statement is false.
Noise pollution may cause partial hearing impairment. Yes, absolutely right. Noise pollution can make us deaf either permanently or temporarily.
So it can cause partial hearing impairment. If someone is talking to us, we won't be able to hear clearly. ki bo kya bol raha hai, humein kuch kuch thoda bohat hi sunaai aayega.
That is known as partial hearing impairment. So I hope this is clear. Next, fill in the blanks with suitable words.
Time taken by an object to complete one complete oscillation. Kitna time liya jaata hai? That is known as time period. Next, loudness is determined by, we had read that the more amplitude the sound wave has, the more loudness it will have.
The unit of frequency is hertz, we have studied. Unwanted sound is called noise, we have studied. shrillness of a sound is determined by the frequency of vibration. So we know that pitch determines shrillness and that is directly proportional to frequency.
proportional to frequency of vibration. So, that's why pitch is a shrill voice. Like if I talk about a bird chirping is also shrill.
So, that is determined by frequency as we have read. Next, a pendulum oscillates 40 times in 4 seconds. So, 40 times in 4 seconds. So, how much in 1 second? That will be its frequency.
Because we know frequency. is number of oscillations in one second. So, if 40 times in 4 seconds, then 10 times in 1 second. So, what is your frequency?
10 Hz. Because frequency unit is Hz. And what is time period?
1 upon frequency. That is 1 upon 10. That is 0.1 seconds. Because we know what is time period unit? Seconds.
So, the answer is 1 upon frequency. 1 by 10. 0.1 seconds. Next question. The sound from a mosquito is produced when it vibrates its wings 500 vibrations per second.
What is the frequency? 500 Hz. Because it is given as 1 second. What is the time period?
1 by frequency. What is 1 by 500? 0.002 seconds. Because time period is in seconds.
Identify the part which vibrates to produce sound. So, the membrane above the throat vibrates. So, stretched membrane.
Sitar. We know that like a guitar, strings vibrate in a sitar. So, strings vibrate. And next is flute.
So, if I talk about flute, there are many air gaps in between which we call air columns. If we talk about air, vibrations travel through them. So, musical sound is produced.
So, that is why. You must have seen that Flute is a basuri. Basuri has round holes.
Through those, vibrations pass through the air. And that is called air column. Through which musical sound is produced. When these vibrations go through the air.
So I hope this is clear. What is the difference between noise and music? Can music become noise sometimes? So, what is the difference between noise and music?
We have already read noise, it is an unpleasant sound. Music is a pleasant sound. music causes pollution, music does not cause any pollution and noise is unwanted noise for us. impact on our health like hypertension, lack of sleep. But music is good for our health because it calms us mentally.
Then if I talk to you, do you need any instrument to produce noise? No, they produce automobiles outside too. But To produce music, we have studied a lot of musical instruments like sitar, tabla, guitar, violin, etc. So I hope you have understood the difference. List sources of noise pollution in your surroundings.
Loudspeakers, loud music, honking of automobiles, if there is a traffic jam, we hear this sound again and again. horns continuously press so that is known as honking of horns. The cars that pass by generally produce sounds from the engine.
Again if there is a marriage or if we consider the time of Diwali, then continuous sounds are heard because the crackers keep on blowing. They are known as explosions. So all these things are sources of sound in our surroundings.
Explain in what way noise pollution is harmful to human beings. So we have studied that noise pollution, lack of sleep, hypertension, temporary or maybe permanent hearing disability, all these causes us. So these are the ways in which it is harmful. Your parents are going to buy a house. They have been offered one on the roadside and one which is three lanes away from the roadside.
So which one would you prefer? The one three lanes away or the roadside one? How will the roadside person prefer? If you take a house near the roadside, what will happen?
The sound of cars coming and going will come and your lack of sleep, hypertension, all these things will start. So that is why what do we do? We prefer that we take a house in the back lane leaving three lanes from the main road so that we can avoid the harmful impact of noise pollution.
sketch larynx and explain its function so larynx is a voice box it has vocal cords two in which there is a slit when air passes through the lungs slits, then those vocal cords vibrate and produce sound. So I hope this is clear to you. If we want to know about the structure of the larynx, then we know that the present windpipe upper end is present there and what happens in the larynx?
there are two vocal cords what is produced by their vibration? sound is produced now two muscles are also attached to the vocal cords if those muscles are tight then the sound produced will be different and if those muscles are loose then the sound produced will be of different quality so the sound produced by all the people will be slightly different If I give you an audio clip and tell you which actor's voice is this, then you can recognize it because everyone has a characteristic quality. So you can decide on the basis of that quality. So I hope these questions have become clear to you.
So these are the solutions of class 8th science chapter sound. Now the most important question is coming. You must have observed that lightning is seen first and thunder is heard later.
Why is that? Of course, thunder should be heard with lightning. Why is that?
Lightning is seen first and thunder later. So for that I will... I would like to tell you that the speed of light is 3 x 10 to the power 8 meter per second. This is the speed of light which we denote from C.
And this speed of light is 10 to the power 8. Which means that it happens millions of times. So, before we see the light at such high speed, it takes time for sound to travel through the air. Because the speed of sound decreases with light.
So, we see the light first, we don't see the light first and the sound of thunder. So what is the reason? The reason is that light travels faster than sound. So I hope you have understood all these questions of NCRT and they will be helpful for you.
So in our next video, we will study the next chapter of class 8 science. Till then, Thank you.