0:12 Hello children, good evening, I am Gopal sir, once again I am live among all of you children and I am starting with the chapter that you all were waiting for, children, and the first one is our one shot and today's class will be complete on propagation of light, but what will we teach children, today we are going to teach you propagation of light and it is going to be a very important class and I have told you that in the coming seven days, once the class is over, we will finish it there and the next day we will study further in the new class, okay, so let's start children, today's class is a very important class of class 12th Physics propagation of light and this class is going to be very interesting for all of you children, so let's start, let's go, before starting the class,
0:59 I want to tell all of you children that such children who are absolutely new in our class, such children who are absolutely new in our class, who have just joined, all those children should first of all subscribe to our channel, the name of the channel is Gopalsar Physics, you will subscribe children, okay, as soon as you subscribe to the channel So don't forget to press the bell icon button because from here children you will get notification that our class has started and after that children like the class, it is okay, share it with your friends as much as possible, comment how you liked the class that is going on, what are the topics that you want to study more, so
1:46 children you can tell us all these things by commenting, okay so let's start, remember all these things, then we will talk children, let's provide PDF to all of you children absolutely free of cost, we have a Telegram channel, the name of the Telegram channel is also Physics and here you get PDF of all the classes absolutely free of cost, along with this, notifications of classes are also sent here that when are the classes starting, when is your class coming, at what timing is it coming and you will get a lot more on our Telegram channel, so you can also join the Telegram channel, okay so the name of the Telegram channel is also Gopal Sir Physics, you should also join this children Okay, then let's move ahead, so
2:34 today we are going to start with optics of light, where we study about the phenomena related to light, refraction of light, reflection of light, interference, reflection, polarity, we study all these phenomena, children, what do we call it, we call it light, did you understand the point, where the phenomena related to light, refraction, reflection, reflection, polarity, all these are studied, children, it is called ray of light, light is mainly divided into two parts, which are your two chapters only, the first thing that we study about light, children, is what is ray of light, first of all we study about ray of light, where the study of light is done in the form of ray, it is called
3:21 ray of light, okay, and the second one is wave of light, okay, the second one is wave light, children, what is it called wave light, so we have two chapters, you should know very well, okay, we have two chapters coming, these are in your book, chapter number nine, chapter number 10, so today we are starting about light, then after this, in the next chapter we will
4:08 teach you about light ok, reflection of light, the reflection of light, so the light after striking a surface returns back to the same medium is called reflection of light, what actually happens kids, when the light hits a shiny surface, kids, when the light hits a shiny surface, kids, the light returns back to the same medium, in this way the ray of light returns back to the same medium, this
4:54 phenomenon is called reflection of light, okay, this ray which comes on the reflection page, kids, what is the name of the ray, kids, it is the reflected ray, we call it, kids, what do we call normal, kids, we call it normal, sorry point, and the lambda drawn at that point, kids, what is
5:40 this perpendicular called, kids, now make a corner between the incident ray and the normal, kids, make a corner between the reflected ray and the normal, kids, and this is the phenomenon of reflection of light, it is very easy Okay, kids, when a ray of light falls on a bright medium, it returns back into the same medium, this is called reflection of light. The light ray that is coming is called the incident ray and the one that is emerging is called the reflected ray, what will you call it, kids, that is called the reflected ray, okay, what is it called, it is called the reflected ray and kids, what do you call the normal drawn at our point? The angle drawn at the incident ray and the normal is called normal, and
6:27 what is called between the incident ray and the normal, kids, is called reflection, okay, absolutely, you can note the definition from here, it is represented by I, reflection, what is called the angle between the reflected ray and the normal, kids, we call reflection, it is represented by small R, okay, is this clear to you, are these topics clear to you, read one more thing here, kids, laws of reflection, how many laws are there of reflection, two laws of reflection There are rules, the first rule says that
7:13 children should always remember that what happens is equal, children, equal means that children are on the same plane, have the same resolution, okay, it is clear, all of you children have to remember these two rules, if any child has any doubt in this, then you can ask, these are very important topics of light which are very important topics of optics, children, and you have read all this many times in class 10th also and all these
8:00 can be asked to you in exams in class 12th also, you should remember this thing, as we move ahead, children, the most important thing here is the mirror, children, the most important thing here is what is that, children, it is a mirror, okay, what is that thing, it is a mirror, so what would you like to read in mirror, what is a mirror, children, mirror is a person who reflects all the light falling on him, children, what kind of a device is a mirror which reflects all its light It gives tendency to reflect light. That is why when we look at our face in the mirror, our face is clearly visible. Because everything is fine.
8:48 Children, whatever is to be reflected, we can say whatever is falling on it, it gets reflected. That is why we can see our face clearly on the mirror. In practice, it is glass. Children, in practice, a mirror is made by coating three layers of mercury compound on glass. And what is the reflecting surface of the mirror? It is very shiny. There are mainly three types of mirrors. One is a flat mirror. Children, what is the reflecting surface of the mirror? Children, what is it called when the reflecting surface is flat? Children, what is it called? It is a plane mirror. Children,
9:43 remember this. What will be the reflecting surface of the mirror? Children, it will either be raised, what will it be called? Children, it will be raised, what is it called? Children, these are called round mirrors. The first one which is raised or in a shape, what do we call it? Do you know, it is called a concave mirror. Children, what is it called? This concave mirror and the one which is raised Children, that is called the answer
10:30 mirror and these two which are there, children, what are they called, do you know what these two make together, they are called bullet mirror, what are they called, children, tell me these two are called mirrors and one is of parabolic shape, children, it is of such a shape, what is it called, children, this is of parabolic shape, remember this, I am starting from the very basics,
11:19 okay, let's talk about this, children, what do we have to read in this chapter, what do we have to read about bullet darpanon, tell us what do we have to do about darpanon, we have to read, okay, children, we will read about bullet mirror, so what is called a spherical mirror, bullet mirror is called a mirror whose reflecting surface is, children, it is round, okay, now tell me concave and one is the answer concave mirror, listen once again, such a mirror whose reflecting surface is bulged or sunken, children, what is that mirror called, it is called concave, the reflecting surface will be something like this where
12:06 Children, what will be the reflection of light from this mirror? Children, which mirror will it be called? This is called a concave mirror and this is called a concave mirror. Children, what is the reflection of light from this mirror? Children, concave mirror and a concave mirror, you should always remember this. This is very important, it is very important, it is clear.
12:57 After this, children, you have read the following rules for creating an image from a sphere mirror many times. I am revising the whole thing to you once that how, it is important for you to remember it so that when you make it in future, children, everything becomes very clear to you. So, children, what are the rules for creating an image from a sphere mirror? The first rule, children, the first rule says that the light which is incident parallel to the principal axis, goes through the main focus in the concave mirror or appears to be coming through the principal focus. You will see the diagram in the acave mirror, everything will become clear to you. Children, such a ray of light which is coming parallel to the principal axis, how does it pass through the mirror, from where does it pass It goes through the principal focus,
13:43 from where does it go, children, it goes from the principal focus, where does it go in the concave mirror, okay, where does it go in the concave mirror, okay, you should always remember this thing, I will make it and show you, will you wait for a minute, let me make this thing and show you, okay, I will make this thing and show you how your diagram will be made, we will make this diagram here and show you how these diagrams are made, see how they will be made, children, what do we
14:32 call the first rule of creation of a mirror, which falls parallel to the principal axis, the light which falls parallel to the principal axis, goes through the principal focus of reflection, if I take an example of a small concave mirror here, children, what do I take, I have a concave mirror, children, a ray of light which is coming parallel to the principal axis, then as soon as it gets reflected, where does it go in the concave mirror nearby, okay, answer What happens in the mirror, it appears to be
15:19 coming through the main focus, from where does it appear to be coming, children, it appears to be coming through the main focus, in which case does it happen, in the mirror, okay, in which case, it is not visible clearly, what happened,
16:33 from where does it go through the main focus, children, does it get uprooted from the main focus, in the concave mirror or where does it appear to come through the main focus, children, in the mirror, I will just explain to you here for both, okay for the mirror and for which children, the one which is concave, I will also tell you here, okay, how will yours be, which diagram will be formed, children, if we have a concave, now we will talk about the mirror, okay, which one will we talk about, children, look at the mirror, what happens in the mirror, let's see comfortably, what happens in the mirror, children, if any light is parallel to the light, then
17:20 what happens in this way, it gets reflected, so how does it appear, it appears to be reflected, how does it appear, children, it appears to be reflected through the main focus It is visible, okay now it is clear, the diagram is visible, isn't it clear? Let's go
18:06 here once again, okay, we are making a concave mirror, which passes through the light in the concave mirror, if this is the main focus of the concave mirror, children, it is incident through the main focus, you will see the arrow mark, how does it go, children, how will it go parallel to the principal axis, children, it will go parallel which will come above the main focus, see the arrow mark, children, this arrow mark in the ray of light is very important, if it is passing through the main focus, then how will it go, children, it will go parallel to the main axis, where in the north mirror, okay and after that, where is the concave mirror, sorry children, this is your
18:53 north mirror in this concave mirror, children, okay and what is this, children, we have a concave mirror, then next see children, the next diagram, okay, this is done, we have it, now see from here, what does it say, where does the light ray fall in the direction of the main focus, let's say there is a light ray, children, going in this way towards the main focus in the direction of the main focus, what will happen to the side of reflection from the lance, children It will go parallel to the principal axis, it is easy, everything is fine, did you understand the point,
19:40 whatever happens through the principal focus in the concave mirror or towards the principal focus, where children, in the north mirror, that side of the reflection goes parallel to the principal axis, both the rules, children, are exactly opposite to each other, how are they opposite, they are opposite, the light ray that comes parallel to the principal axis goes through the principal focus and the light ray that comes through the principal focus and falls through the principal axis, goes parallel to the principal axis, the sides of reflection, okay, it is clear my man, those who are not able to see, they should increase the quality of their video, whatever your class is, children, then only you will be able to see, okay, let's move ahead, children, the side of reflection that happens through the centre of curvature or towards the centre of curvature,
20:29 returns back through the same path, such light, children, okay, I am telling you once again by taking the example of a concave mirror, such light, which goes through the centre of curvature, such light, which goes through the centre of curvature, it returns back through the same path What happens in it, children, it returns back, what happens in the same path, children, it returns back, okay and one last thing, children, the light which falls on the pole, all such types of light which fall on the pole, this pole is the middle point, children, the pole is the pole, what happens to it by following the rules of reflection, children, it gets reflected, this has
21:14 come to us and what happened to this reflection, children, what happened to the reflection, you should remember these four rules very well, in the first rule it was told that children, if the light falls parallel, then it will go through the focus, in the second rule, children, if it falls from the focus, then it goes parallel, in the third rule it was told that it will go through the centre of curvature, then it will return back in the same path and then in the next rule we told you that the light which falls on the pole, what happens to it by following the rules of reflection, it gets reflected, you should remember these four rules, okay, let's go, did you understand? Ok, let's
22:01 talk further, children, how is an image formed by a concave mirror? What do we do with a concave mirror, children, how do we form an image? Okay, so when you form an image by a concave mirror, what do you do with an concave mirror, children, you form an image? Okay, so the position of the object, okay, the position of the object, understand my point, okay, so see the position of the object, I am telling it here in a shortcut, you guys remember how an image is formed, how is it formed, this is also very important to you in objective type questions, children, it can be asked, so pay attention to what I am saying, when the object is at infinity, then where is the image formed, children, at the main focus, when the object is at infinity, then the line of light comes
22:46 parallel to the principal axis, then from where does it go, it goes above the focus, children, so if two rays of light are coming parallel to the principal axis, then where is its image formed, children, at the focus, where is it formed, children, when the object is at infinity, then the image is formed at the main focus How is it formed at the focus, children? It is very small, exactly the size of a point, it is very small and real, and how is it formed inverted, children? It is real and how is it formed inverted, children? When the object is between infinity and centre of curvature, then the image which is formed between centre of curvature and principal focus, children? Smaller than the object, real and inverted, the one which is important, I will ask you to pay more attention to it, it is important,
23:32 children. First number will be at infinity, so where is it formed at the principal focus, a very small point in the shape of a point, real and inverted, in important children, your third number is formed when the object is at the centre of curvature, children, the representative of the shape of the object is formed at the centre of curvature, children, it is formed real and inverted. Some points are such which are asked a lot in exams like the third point, when is the image of the object of the same shape formed, when is the image of the object of that shape formed, when is the object at the centre of curvature, when is it formed, when the object is at the centre of curvature, children, where is the earth formed, children, where is it formed at the centre of curvature, children, that story The centre is formed of the shape of the object, it is formed
24:19 real and what is formed, children, it is formed inverted, okay, you should always remember this as we move forward, children, number six, okay, the curvature is formed between the centre and the principal focus, so the curvature is formed between the centre and infinity, larger than the object, real and inverted, okay, it happens at the main focus, children, so the inverted of the first one at infinity, when it was at infinity, this is also an important point, isn't it? Fifth number five is also an important point, I had read earlier that when the object is at infinity, the image is formed at the principal focus, read this here, children, when the object is at the principal focus, then where is the image formed, how is it formed at infinity, how is it formed from the object, children, very big, real and how is it formed, children,
25:04 inverted, real and how is it formed, children, inverted, this thing you should remember, okay, number six, between the main focus and the pole, how will it be formed between the main focus and the pole, behind the mirror, how will it be formed behind the mirror, children, how will it be formed from the object, how will it be formed bigger, you will laugh and how is it formed, children The shadow is also important, children, this is also the only condition when the image is virtual and straight and this cannot be achieved on the screen, where is it formed, children, when it is between the main focus and the pole, where is it formed, it is formed just behind the screen, but see how it is formed, children, how is it formed behind the mirror, it is
25:50 bigger than the object, virtual and how is it formed, it is formed straight, so these are some points, okay, you should always remember them, okay, these are some points, children, you should always remember them, now the children, okay, a lot of children requested a lot, sir, you should teach chapter nine, I have brought chapter number nine on your request, come brother, I will read chapter number nine, but all the children here, today, all the children who are watching the class, I am feeling very disappointed, I am feeling sad, it seems that the children do not want to study at all, friend, okay, children do not want to study, they come to this class to pass their free time, I am telling you a very small but important thing,
26:36 okay, I have forgotten this thing again and again, my point Listen very carefully to this year, do you know which year is going on? 2000-22 is of the most importance for those children who are in class 12th. In class 12th, all your studies, your earning of that life, it takes only one year. Class 12, if you study this year and do something good, then consider that your life is successful. You will never need to be disappointed in life. You will never need to accept defeat in life. One year is not even left now. Only a few things are left. These few things can make your life very good or
27:23 spoil it. It is only important to be careful about your studies. The child who at this time will only spend time, will not study the last few things, will not be able to move ahead in life at all. So, you should absolutely study every thing. You should try so that you can do much better, you can study very well, remember this thing, we are saying this again and again, we are saying it many times, this is being said for your good, so you should pay attention to this, okay, remember this, son, the number of children is very less, very less, let's listen, how is pratinid made by the mirror, children, there is only one
28:10 condition, the mirror is made by the mirror only like this and there is nothing in it, children, look here carefully, I am taking the mirror, what is the mirror, whose reflecting surface is like, it is raised, what is that mirror, children, the mirror, whose reflecting surface is like, it is raised, how did the first light ray go parallel to the main axis, children, let's listen here, I will make an object and show you, we assume here, children,
29:00 how is a light ray going above the children, parallel in this way, from where does it pass, from where does it appear to come, children, this happens from the focus of the mirror, once again I want to explain this, let's see what happened Children, I had told
29:46 you where is the object? It is placed right in front of the principal axis. What is the name of the object? Children, now a light goes parallel to the principal axis. Children, it gets reflected in this way. It went this way and what happened here. So when it gets reflected, children, it seems that this reflection is taking place from where. It seems that it is happening from the main focus. From where does it seem that children, it seems through the main focus. Listen to me carefully here, near us, where will the second light ray go? The second light ray went in the direction of the centre of curvature. Children, it
30:42 goes in the direction of the centre of curvature. It returns back in the same path. We have moved ahead from the dot-dot line. So here, children, on the other side of the mirror, the object is smaller than the object. Okay, a virtual and straight image is being obtained. Where is it near? Where is it near? Children, did you understand? Remember, the light ray, children, where is it going? Can you see it clearly? It will work.
31:36 Okay, brothers, everyone should study physics in Bio class. let them study physics, okay, let's go ahead, what's the matter, there is a very interesting topic going on, okay, a very interesting topic is going on, let's move
32:52 ahead, now we will talk children, the relation between the radius of curvature and the focal length of a spherical mirror is a very important, okay, a very important relationship, for whom is a concave mirror, for whom is a concave mirror, for whom am I showing it, for whom am I showing it, for concave mirror, okay, look very carefully, I am showing it, so if we draw this for a concave mirror, then how will it turn out, children, look carefully, first of all I want to make a concave mirror here, what will I make, children, I am a concave mirror,
33:41 first of all you should understand our diagram children, this diagram properly, a light ray which is incident parallel to the principal axis, this is the principal axis, this
34:27 light is incident parallel to the principal axis, we have named it children, now what name have we given it children, now the light ray which is incident parallel to the principal axis, I You know what it is, kids, what it is, okay, where does it come out of the side of refraction of the lens, kids, it passes through the principal focus, from where do the lenses go, it goes above the principal focus, here kids, I draw the centre of curvature, I draw a normal, kids, from where does it come out from the centre, okay, this is the normal which is passing through the centre of curvature, so what will happen to this which is made, kids, it will happen to us and what will happen to this reflected ray, kids, what will happen to the reflection, it will happen to us,
35:12 okay, this is how you understood the diagram, it is a very simple diagram, okay, I have made a very simple diagram for you, kids, I have given you a very simple diagram, okay, you should always remember this, the relation between the radius of curvature and the focal length of the spherical mirror, for the concave mirror, I started drawing the line from here, okay, one ray of light went parallel to the principal axis, it passed through the focus, the second ray of light from the centre of curvature, this ray of light, sorry, this is the normal, kids, which is passing through the centre of curvature, what is this We have the normal, this is our angle or refraction. So let's first listen to it, okay, first of all, children,
36:00 what will happen to us by the rules of refraction. What will happen to us by the rules of refraction? So look here, we have to see which angle ABC will become, children, which angle ABC will become equal to, which BF will become, children, which BF will become equal to, children, which BF will become equal to, children, which BF will become equal to, what equation number one did we have, children, what equation did we make, children, we have made one. Now, we have to see, children, P, so here we will see
37:09 what we got from this, look carefully, okay, ABC ABC will become equal to, which BCF will become equal to, how are these two, children, these are at alternate ends, okay, which are these, children, these are at alternate ends, what has our equation number become, okay, what has our equation become, okay, further we will see, children, from where from equation one and from where from equation two, equation number one and equation,
38:05 both these angles become equal. Which two angles? This angle and this angle, children, both of these are equal to each other. Okay, you must have read a theorem regarding triangles. Children, if the sides of a triangle facing each other are equal, then the opposite sides of it facing each other are also equal to each other. Which one is in front? Look, these are equal to each other. I have put a cross on this angle. Children, so what will happen, the opposite sides will also become equal to each other. Okay, so we will write it here. Children, so which triangle? Children, we can write CBFC. What will happen, children, this CF will
38:50 become equal to the FB of which child? Children, you can take this as question number three. Okay, we will write it here. Children, because, okay, how is the mirror's view, children, the view is very less, if we take it
39:37 equal, what will happen, children, so if we take P and B equal, then what will happen, children, this PF, children, what will happen to the BF, children, it will be equal to equation number four. Now look at each name, give it FB FB. I will give it to you, is it okay or I will give the names of BF, there should not be any confusion, equal is given, the names are okay, now here if we see equation number three and equation number four, children, look again, if each side becomes equal, then what happens, we have Cf equal to whose PF is less, children, whose PF is less than whose PF is equal to PF, if here
40:24 children, I add PF in both the animals, this is Cf = PF and here also I will do PF plus, okay, let us write here, what do we add in both the animals, children, on adding PF in both the animals, what did we add in both the animals, children we have added PF, okay, this is okay, now we have added it, so what does Cf + PF become, children, what will happen to us, cf+, children, what will happen to us, c and PF + PF, children, if you see the distance between C and P, children, so this is the radius of curvature, what is this thing, children, this is the radius of curvature, this is r, then the minus will
41:09 come and PF, this is the focal length children, this is also a and, so what will come to this also children, minus So, children, I will write CP as R. You will write PF as F = Those who read with utmost honesty and read very well, did anyone
41:55 understand this? Does anyone have any doubt in this? What did I tell you about the sphere mirror? Children, I told you the relation between radius of curvature and focal length. Children, what did I tell you about the sphere mirror? Children, tell me the relation between radius of curvature and focal length. Okay, this is okay. I told you for concave mirror. Okay, I told you for concave mirror and it is very important. Children, r/2 is Okay, it will work. Look here. Children, find out the focal length of concave mirror and concave mirror. It says that if the radius of curvature of each is 20 cm, then we can do it one by one. Children, first of all, for which mirror can we do it? Children, first of all, I will go for which mirror? Children, for which concave mirror, for concave
42:40 mirror, the radius of curvature for concave mirror, R, you always take it as negative -20 cm. If we talk about focus, then r/ will be A. Children, you will go for A. The formula will be -20/2 = -10 cm. From here you can remember that the radius of curvature and focal length of a differential mirror are always negative and the formula is very easy. By the way, if you go to the second number, for which children, for the north mirror, for which children, let's go for the north mirror, then R = ok, how much will it be in centimeters, okay,
43:32 20 / 2, okay, how much will it be, children 10 f = 10 cm final f = 10 cm, children, here you have to remember this thing, son, how is the radius of curvature and focal length for a concave mirror, is it positive, how is it positive, children, you have to always remember this thing, it is clear, I am telling you what is mirror formula, it is called mirror formula, mirror formula, children, the formula showing the relation between the distance of the object from the mirror
44:18 u, the distance of the object from the mirror and its focal length u, we call it mirror formula, the equation coming in relation to a round mirror is called mirror formula, what is this formula, children 1 / f = 1 / v + 1 / u is the mirror formula Ok, what is this? Children, I will prove it by showing the mirror formula. Mirror formula is for concave mirror. For whom will we do the mirror formula for concave mirror? See, mirror formula. Mirror formula for which mirror will we do it? For which mirror will we do it? Children, we will do it for concave mirror.
45:12 First of all, pay attention to the diagram. How will the picture look? Children, we have a concave mirror. Okay, this is its principal axis. Children, what do we have? Concave mirror, its principal axis is here. Children, here a light ray is coming. Look carefully here. There is an object on the principal axis. Name the object. Children, now where is a light ray located and it is getting reflected following the rules of refraction of light. Where did this light train go? Children, it came to the pole and this was refraction. Did you understand
46:02 where is the light ray going? Children, on the pole, I had told the rule that whenever a light ray goes to the pole, what happens in the same direction? Children, it gets reflected. Okay, what happens in the same direction? Children, it gets reflected. So, this is the angle children. And what did this make of our eye? Okay, so now I have my eye and what happened to this, children, what happened to the reflection, we have R, okay, eye is done and what happened to this, children, it has become R. Now the second light ray, children, the second light ray, from where will it pass, it will go above the centre of curvature, from where will it go above the centre of curvature, children, I had told this that the light ray which goes through the centre of curvature, what happens in the same path, children, it returns back and at the point where these two rays cross each other, a smaller and
46:49 inverted image of the object will be obtained, so what are we getting, children, one light ray went through the pole and got reflected following the rules of reflection, children, and the second light ray continuing above the centre of curvature, what happened in the same path, children, it returned back, where both of them cross each other, we got the inverted and real image of the object, what happened, children, we got the inverted and real image of the object, ok, let's talk, children, how will we prove this, how will we prove this, listen to me carefully, okay. Here we can see two triangles, triangle ABC and triangle ADE. This is okay, so here we will take children, triangle
47:36 ABC and triangle ABC and triangle C. How are both these triangles, children, are they similar triangles? Children, how are the triangles similar? The ratio of corresponding side, this now, children, will be upon A dis, okay, will be equal, children, what will happen to us, children, the ratio of E to B will be in the ratio of B-C. These are question number one
48:42 similar triangles. If both of these are also similar triangles, then we will take children, the ratio of corresponding side, this will be now and this will be abroad, children, okay, and this will happen to us, children, video B. This will become equation number you, what will become equation number two, children, what will become equation number two, okay, equation one and this equation number two, if we do equation one and equation two by two,
49:46 okay, how do we change it, okay, so what can we write for e, children, this is what we have, ee, what will we write for e, children, I will write e as b - look, this is e, how will I find out e, this is this much distance e, so if I minus the PC in b, then I will minus the PC in b, children, then my e will come out in the same way for b-c, children, I will minus the PC in PC, okay, children, I will minus the b desh, okay, this is what I have written, children, I will write down the BP that I have written here, b and I will write this, children, PBS, in this way, you have to find out the value of e,
50:32 how will you find out e, PV - PC, then e will be left, by the way, how will you find out b desh c, children, what do you have to do, PC minus b desh, it will come out here, it is very easy, look PV, I am telling you all the values, b, this distance from P to B, children, this is measuring the distance of the object, it is telling the value of the radius of curvature r, children, this radius of curvature which is telling the distance of the image, so the distance of the object b PDS, what is the distance of the image PC, children, keep all the values of curvature r and all the brothers All the marks will come, minus P will also be what is the distance of the object, children, so - minus PC minus R A is okay,
51:17 PC children, minus R has come, minus PDS, this is minus C, children, PV children, - U has come and what is P B des, children, -3 has come, in this way you keep all the values, let minus U plus R - U + R - R plus minus will cancel U / V will become V and this will happen from here you will do cross multiplication children - uv plus what is A, children, 2vf is okay, equal A will happen, children, we will have -2m,
52:10 okay, in the next step you do one reduction, children, bring this -2f here, bring -2 off here, children, what will happen, you have 2vf, so if you bring the minus one, it will become plus, children, you will become U F and we will take UV there, how much will UV be, you will become U V, okay, you will become U V 2 2, so it gets cancelled children, you will cancel from both sides, so This will be left with us. If we divide VF plus of = uv, then it will become VF / uv. Okay, it will be
52:59 equal to A, kids, after cancelling everything out, if you come to the final equation, then look there, on the right hand side, what is left? 1 / f. Here, what is left, kids, 1 / u and here, what is left, kids, 1 / v. So, we have the formula 1 / f = 1 / u + 1 /. What happens, kids? Did
53:49 you understand this? Do you always remember this? Kids, what is the mirror formula? What is this, kids, the mirror formula? Okay, let's move ahead. What is the next topic, kids, we have a very simple topic of linear magnification, the length of the image and the length of the object, m is equal to this. Kids, the length of the object is represented by I and the length of the object by O. Okay, and kids, if we get the minus here, we will also represent it by V/u. M = I / O = -V / u. This is the formula you have. Okay, now whose turn is it, kids? We have some very important questions. Okay, which you should solve very well, let's see how many children can answer the first question, question number of quiz van, quiz van children, question
54:35 number van, okay, the pole will come on the pole, you have to keep giving your answers, okay, the first question, question number van, a light ray is incident on a mirror, what will be the magnitude of the reflection, children, if a light ray is incident on a mirror, then what will be the magnitude of the reflection, what does it seem, a light ray falls normally on a mirror, if this is a mirror, children, what is this, is this a mirror, okay, what is this, is this a mirror, children, the light ray which is incident on it, then
55:22 how much will it be reflected, what will be the magnitude of the reflection, children, what will be the option, see zero light mirror is installed, children, which mirror is installed in front of the driver of a motor vehicle,
56:09 plane mirror, north mirror, what is a concave mirror or north lance installed, which mirror is installed, the drivers of the motor vehicle Children, a plane mirror is placed in front of it, north mirror, concave mirror or north lance, what is placed, which one is placed, exactly the north mirror, because what kind of image is obtained, children, what happens to the virtual and the object, it was very small that we should see clearly what to do, okay children, what will we do here, we will end today's class and before leaving,
56:54 children, once again I would like to tell all of you children that you should subscribe, okay, thank you.
