 Only chapter in the class 11th that does not talk about study of matter or mass, everything else talks about study of mass, fine. This is the only chapter at the end they have kept it, okay and here we are going to discuss about something which is very very important for our day to day life ways, okay. Now what comes in mind when you hear waves as a like nice as a sine wave comes in my mind. So sine wave is a very very special kind of wave, okay it is not that all the waves must be having the sine form, okay. So and at the same time the waves can be of like whatever we have discussed in terms of shape there can be multiple shapes possible, okay. It can be the weirdest possible shape you can imagine that can also be you know treated like a wave, okay. The kind of waves can be categorized into different different types, okay. So when it comes to categorization you can divide them into let us say some there will be some type of wave that do not need medium for them to travel, do you know what kind of waves there are? Electronica. They are EM waves. Please write down EM waves, EM wave, okay it is like you do not need a car to travel you can walk alone, fine. Similarly EM wave they do not require anything for its travel from one point to other, okay. So when it comes to EM wave or any kind of wave I am saying traveling, what does traveling of wave means? Traveling from one place to another. Do not tell me synonyms, okay. Traveling of waves means what? Going from one place to another. Going from one place to another. What goes from one place to another? Wave. Wave goes? Disturbance. Disturbance goes from one place to another. What do you mean by disturbance? Energy of information. Disturbance is what? Disturbance is anything whatever was not happening earlier at a particular place something else has happened there you can say that it is a disturbance, okay. Now since there is a medium which is elastic in nature it will be like as if it got stretched a bit so there will be a potential energy also. And when there is a disturbance something is moving so there can be kinetic energy also. So you can you know loosely say that the disturbance has kinetic energy and potential energy, fine. Now when I am saying this disturbance travels what you are talking about is transferring the kinetic energy potential energy from one point to the other point, okay. Now the mechanism of transferring energy from one point to the other point only one thing we know till now is collisions, right. One ball comes, one mass comes and collide the other mass and transfer of energy happens and the other ball also starts moving, okay. Here is one method in which you do not need to touch that point. You can do something over here and energy can get transmitted there, fine. This is what the wave is all about, okay. E-M wave do not need any medium for its propagation. I can generate E-M wave over here and it will travel there irrespective of whether there is a vacuum or something else over here, fine. So this is E-M wave and you cannot imagine your life at least without E-M waves because this will enable you to play games, this will enable you to watch television, internet and everything else is due to the E-M wave, okay. And the other kind of wave that needs medium for its propagation is what? Sound wave is an example of that kind of wave, mechanical wave, okay. Mechanical waves need medium for its propagation. It cannot walk alone, okay. It needs medium. Now, one example is sound. So basically, if you are in vacuum, you can't speak. You can't transfer information while speaking to the other person. They will be just live movement, sound will not be there, okay. So can you tell me any other example of mechanical wave? Distributes from one point, traveling to the other point, using medium. So water wave. Water wave, you throw stone on the water, okay. So you can see that ripples get generated. It goes from one point to the other point in a form of concentric circles, okay. Now, when the disturbance is going from one point to the other point, is the water going from one point to the other point? But it looks like so, right? Water is rising, so keep throwing water. There will be a huge ditch in between and water will reside, okay. But it just appears like that, okay. It is a disturbance that is moving. So water near the land doesn't know that you have thrown stone in the middle. But are there some time that disturbance traveled near the land also, okay. So this is another example of the mechanical wave. Any other example you can think of? Spring, like what? If you pull a spring on one end. So if I have a spring like this. If I do like this, okay. The spring will oscillate like that and this oscillation will travel, right. Anything else? So if you have a ribbon and you just kind of move it up and down. Yeah, ribbon is there. You can just tie one end of the ribbon and just move one end up and down like that. There would be ripples that get generated on the ribbon itself, okay. So the example of a ribbon is an example of one dimensional wave. Okay, it is the velocity of the wave is only in one straight line. That is what it is called one dimensional, okay. There will be two dimensional wave. What is the example of two dimensional wave? What the ripple is a two dimensional wave. The velocity will be on the surface and it is going to spread on a single plane, two dimensional. Three dimensional wave, some with three dimensional wave. So when I speak, if you treat a mouth as a point, this thing, then sound is getting spread in a sphere. Just like water ripple gets spread in a circle, sound spreads as if it is in a sphere, it spreads, okay. So this is part of our class 11th curriculum. Mechanical wave. This you are going to learn in 12th, fine. Yeah, gravitational wave? That's a 4D wave. We are not going to discuss that, okay. So mechanical waves, we are going to discuss in this chapter in greater detail. But before we even get into the, what is a mechanical wave and things like that, I need to first understand what is a wave itself, okay. So there will be one section of the chapter that only talks about what is a wave irrespective of whether it is a mechanical wave or an EM wave. So basic, the first section of the chapter is common to all kinds of waves, fine. Now mechanical waves can be further classified into two types of wave depending on how the medium is behaving while the wave is traveling. Are you ready what I'm trying to say? Okay, when it comes to EM wave, there is no medium. But when it comes to mechanical wave, there is a medium. So depending on what medium is doing, when the wave is traveling, you can further quantify mechanical waves into two types, okay. Do you know what are they? Has this chapter started in your school? Longitudinal and transverse waves. Write down longitudinal and transverse waves. Every wave, whether it is mechanical or EM, will travel, right? So for example, let's say if sine wave comes in your mind, let's say this is a wave, part of the wave. This is a disturbance, okay. How this travels? How will this travel? Will this travel as it is? As it is? So disturbance as it is moves forward. So total, how much is the movement? This much is the movement of each and every point on the wave. Are you getting it? Okay, the entire wave as it is, maintaining its shape and size, moves forward. Okay, now while the wave is moving forward, the particles are doing something, okay. For example, the particle over here, right now here, it will have to go down when the wave move forward. So it will come down here. So one will come to one dash, okay. Two will remain there only. Then three, point three will have to move up and reach its new location here, three dash. Are you getting it? Okay, so the particles, the transverse, this wave, when it is moving, you're able to draw the shape because this is the shape of the surface of the medium. Are you getting it? This is the shape of the surface of the medium. Now when, when I'm saying this is the medium itself, each and every point on the wave is, it is belonging to the medium itself. So when I'm drawing a new shape, a white color line over here, a wavy line, then this is the new shape of the surface. So the particle over here came down particle over there, move up, okay. So when this kind of wave move forward, the particles move up and down, okay. Now they are moving in a very synchronous manner. So they are moving like this. It appears as if there is a wave that is moving forward. Have you seen those Diwali lights in which there is a, there'll be LEDs and they'll be just doing on and off. You'll feel as if it is moving forward, okay. You'll feel as if light is moving forward, but that is not the case, okay. So similarly over here, the particles are just moving up and down, but they're moving in such a manner that as if the disturbance travels in the forward direction, getting it, okay. This is the example of transverse wave. This is called transverse wave. And transverse wave need not be sinusoidal. It can be of any random shape. I can say that this is a transverse wave. After some time, this wave reaches a new location like this, okay. It's just a special kind of wave, sinusoidal, that's it. So this is a transverse wave and longitudinal is what? Longitudinal wave, the example is, the example you have given me, let's say the spring is there that is connected to the wall like that. And I have moved the spring like this. I have moved like that and pulled like this. So what will happen? There will be contraction somewhere and somewhere there'll be expansion, right? So let's say this is the zone where compression is there. So this compression is going to move forward. This is a disturbance that is moving forward. Getting it? So what the particles are doing? They are moving like this, fine? So here, this is the example of longitudinal. So in transverse wave, write down the particles of the medium. You write down, below the transverse, you write down. Particles of the medium are moving. Particles of the medium are moving perpendicular to the velocity of the wave. Perpendicular to the velocity of movement of the wave. Longitudinal wave, the particles are moving in longitudinal wave, the particles are moving parallel to the direction, parallel or anti-parallel to the direction of the wave. Parallel or anti-parallel to the direction of wave. Okay, any doubts?