NECO Physics 2026 Essay Revision Optics Projectile Motion Explained Score A 1

Welcome to class today. Today I'll be doing quick revision on certain topics that usually come out in the neo exams for those of you that are preparing for the neo exams for physics. So there are certain topics that they must always come out and you need to understand this topics. So I'll take time to talk about those topics. I'll be talking about topics like light, optics. I'll talk about lens. I'll talk about mirror. will give you shortcut that you can use to know how to answer questions on lens and mirror. So stick around to the end of this video. I'll be talking about electricity. I'll be talking about elasticity. will talk about expansivity. will talk about projectiles. Those are some of the topics will be talking about. want you to stick around. And for those of you that commented on my last video telling me that those that video was quite helpful. want to appreciate you. Thank you very much for dropping your comment. It's quite encouraging and we are encouraged to keep releasing content that will help you do well in your exams. Do not forget if you have not subscribed to our channel to subscribe right now and share this video with your friends so they can also get value from this video. Thank you. So the first thing I'll talk about in this class I'll be talking about lens and mirror. This question says list the properties of image formed by plane mirror. Number one. So list the properties of image form by plane mirror. Now I'm going to use this topic to talk about light and optics. will talk about plane mirror. I'll talk about convex mirror or cded mirrors rather. I'll talk about cded mirrors and I'll talk about lenses as well. Now let's talk about mirror. The first thing you need to talk about when we talk about light, light is form of energy, luminous energy. Okay, that is light energy. And the first point you need to know, they can also ask you to define certain terminologies. So the first terminology is ray. What is ray? Ray is path or direction through which light energy moves. It's path path that light energy light energy or path through which light that light energy moves. Better still, path through which let's put it that way. path through which part through which light energy through which light energy moves. That's ray of light. What is beam? beam is combination. combination of many rays. combination of many rays. So what is ray? What is beam? So if have an if have let's say have ced mirror. have mirror like this. This light ray that enters into it. This is light ray. It's the direction or the path through which light energy travels. So this is ray. All right. But when have combination of rays, have many rays, have other rays, have other rays. Okay. Together they are called beam of light. Beam. So here is beam of light traveling into this mirror. That is the first thing you want to know. The next thing we need to know is this. Let's talk about play mirror. Now, if you stand in front of mirror, okay, you want to maybe powder for the females or for the males before you go out of the room, you want to just check up yourself in the mirror. Now, what is mirror? mirror is an optical material. Before divine mirror, let's talk about what transparent material, translucent material, an opaque material is, they can ask you to write on that. So when light travels through material, when light travels through material and that light can go through that material to the other side, okay, that is what you call transparent material. And because of the light being able to go through, you can see the other side. All right, through that material. For example, glass. If you have glass, you can see the other side of the glass because light rays can pass through. So that glass is said to be transparent. All right. Now, when have paper or have maybe tissue paper, all right? And then if you look at tissue paper, you see that yes, you can there's little level of visual or vision that you can see the other side to level. Meaning the amount of light that passes through it is low compared to that of glass. And because the amount of light that can pass through it is low, okay, you can just see faintly or just minimal vision through it. That kind of material is called translucent. So I've defined the first one transparent. Transparent material is the one that allows light to pass through it. Then you have translucent. Translucent is the one that allows just small amount of light to pass through. Little amount of light pass through. Transparent. Light passes through. And because light passes through transparent, you can see through. Because little amount of light passes through translucent, there is limit to what you can see. And the last one is opaque. An opaque object is one that will not allow light to pass through it at all. Light will not pass through at all. So because light will not pass through it at all, you cannot see the other side. You can't see through it. Example is the wall. The wall. So if look at the wall, because light cannot pass through, cannot see the other side of the wall. So that is an opaque material. op light cannot light cannot pass through at all. Good. Now like you to pause this video and you will quickly do an experiment in your room. If you have glass in your room, if you have glass in your room, try to stand in front of the glass and view yourself. You will see that you cannot see yourself inside that glass. You cannot see yourself inside the glass. Rather you can see the other side of the glass. But take book. Take book and place it behind the glass and try to view inside it. Again, place book behind that glass. Okay? Open the glass. Place book behind it and then try to see try to view. You will see that you are seeing your image in that glass. Why are you seeing your image in that class? Because now that glass has now become mirror. It has become mirror. All right? And that practical will help you to easily remember the definition of mirror. So mirror is here an optical material that will not all right that has at least one surface painted or coated that is mirror. So can define mirror is an optical material. Optical has to do with light. Optical material with at least one or not. It doesn't have to be at least with one surface painted. with one surface with one surface painted or coated. So it could be silver plating, it could be silver that is used to to quote it. It could be darkish paint but it has to be painted. So that will that painting is now an obstruction. It's it's an obstacle to the light that is passing through. So because of that obstacle, the light that is trying to enter that glass will now bounce back. So the bouncing back of that light is what will make your image to be formed on that glass and that is what mirror is. So that bouncing back of light is what you call reflection. Reflection is when light coming from source bounces back to the source as result of obstacle in the surface that the light is directed towards. Are you with me now? So because you remember told you to place book behind the glass because the light cannot go through it has to bounce back and then your image is formed there. So that is how you see yourself in mirror. So mirror is an optical material with one surface painted or coated. For mirror, mirror operates on the principle of reflection. So mirror that is another question you could be asked. mirror operates on the principle of reflection. mirror operates on the principle of reflection. So reflection means the light cannot pass through it bounces back. So if you want to define reflection, reflection can be defined as what? You can define reflection as the bouncing back bouncing back of light rays. bouncing back of light rays to its source to its source. When it falls, when it falls on surface as result of an obstacle, obstacle or obstruction. As I've always said, there are scoring points that the examiner is looking for. So, you don't need to cram what is in your textbook. Once you understand the concept, you'll be able to put it in your own language. There are certain things the examiner is looking for scoring points that will earn you the mark. So when you say I'm bouncing back, that is reflection back to its source where the light is coming from and then it falls on surface bounces back and then as result of an obstacle in that surface, you have captured your scoring point. hope that is clear. that is reflection. So the next thing we want to talk about is let's talk about the types of mirror. We have defined mirror. We have spoken about the principle that operates mirror. What are the types of mirror? You can have plain mirror, you can have cd mirrors. For the plain mirror, the plain mirror, what are the properties of? So they can ask you to list the properties of image formed on plane mirror. Then property of image form done on convex mirror concave mirror which are the major types of conve mirror. So let's talk about that. Let's list the properties of image form by plane mirror. Number one if you stand in front of plane mirror you see that you are having exactly the same size as the image you are seeing. So they have same size. to same size as object. Number two, you'll see that if you go close to that mirror, your image will come close. If you come close, it come close. If you take step back, it goes step back. So, take step back. As you are going farther, the image is going further. So, that means the same distance from the mirror. The image has the the same distance from the mirror as the object. Do you understand? Or object distance from the mirror and image distance from the mirror are the same. So image and object have same distance from the mirror. Next I've discussed same size. The next thing when you raise your right hand up in the mirror you see that in the mirror it's going to be the left hand that is what you call laterally inverted. So it is the image it is laterally inverted. It is laterally inverted. What more? It is virtual image. It's virtual image. What is virtual image? virtual image is an image that is formed when light cannot pass through. Light cannot pass through the image. Light cannot pass through that object and then the image is cast. So it's virtual image not real image. real image light can pass through and then it's far. So but for virtual image light cannot pass through it and then virtual image cannot be captured on screen. It cannot be captured in screen while real image can be captured on screen. So what you have in plane mirror okay is it is virtual. It's virtual image. It's not real. It's virtual image. Same size as the object. Image and object have same distance. It is laterally inverted. It is virtual. It is virtual. One more. Finally, it is upright. Upright or erect. Now, having said this, the next thing want to talk about, let's talk about mirror because wouldn't want to go into details because of time. You know, promise to give you shortcut. I'm going to do shortcut on this board of how to know image formed by concave mirror, concave lens, convex mirror, convex lens. Are you ready for that? Now, before talk about that, it's important to know what is lens. lens is an optical material. optical material with at least one surface curved. At least one surface is curved. So it can be the two surfaces that are curved. Okay, it could be one surface cved. When two surfaces are ced, you can have by concave by convex mirror. If one surface is plain, the other is curved. that is plano concave or plano convex. So lens is an optical material with at least one surface curve. It operates So lens operates on the principle of what? Refraction. Refraction. It operates on the principle of refraction. Unlike the mirror that operates the principle of reflection, lens operates the principle of refraction. So what is refraction? Refraction is the bending or the change in the direction of the light ray. All right? Because of change in medium, material medium. What am talking about? When light is coming from air is going straight or in vacuum, when it enters the lens, lens is glass. So there is change in medium from light to glass. So once that light enters the glass and is coming out it because of the change in the medium there will be bending away of that light ray. So that bending away is what you call refraction. That is what you call refraction. That is what you call refraction. So before we continue let's talk about the laws. They can ask you to state the loss of reflection. The loss of refraction. Loss of reflection. Very simple. There are three things you need to know. Loss of reflection. Three things you need to know. Number one, the incident ray. That's number one. The reflected. That's second. and the normal. That's the third. At the point of incidence, at the point of incidence, all lie on the same plane. Don't mind me. am checking my my microphone because there are times I've done video long time and the microphone had gone off and then just discovered that no sound. So don't want that to happen and that is why have to check from time to time. All right. So the laws of reflection the incident rate the reflected ray and the normal at the point of incidence all lie on the same plane. That is the law of reflection. All right. And then of course the angle of incidence and the angle of reflection are equal. They are the same. The angle of incidence angle of reflection are the same. What's the meaning of angle of incident? This line that comes from the source of light or from the object. This line okay that falls on this mirror. This is the incident ray. So, but to make it lot more clearer, let's do this. Let's have this. So, this is the mirror. normal. This is the normal. Normal is line that is drawn that is perpendicular to the surface of the mirror. Perpendicular to the surface of the reflecting mirror. Okay? Or the reflecting surface. So, this is normal line. So if have an angle of incidence falling here, this angle of incidence, then I'm going to have an angle of reflection like this. Reflection means it goes back thrown back because of the painting here. So when we now say the law, okay, the angle of incidence, the angle between here and this normal is the angle of incident. The angle between here and this reflected ray is the angle of reflection. So this is my incident ray. Why? This is my reflected ray and this line that is perpendicular. Perpendicular means it forms angle 90° with the surface. That is the normal line. That's the normal. So when they say the incident ray reflected and the normal at the point of incident this is the point of incident the point at which it strikes they all lie on the same plane that is the force. And of course the second rule if here is 30° here 2 is 30°. So the angle of incidence and go of reflection they are equal. Right? Now let's talk about the laws of refraction. So they can ask you to state it laws of refraction. It's as well simple too. All right. All you just need to do is instead of reflection reflected here you put refracted. So the incident rate, the refracted rate and the normal the point of incidence all lie on the same plane. That's the law of refraction. The incident rate the refractedly and the normal at the point of incidence. all lie on the same plane. All right. So let's now go ahead and then of course the sign of angle of incidence over the sign of angle of refraction is constant. That is the second which is called the snail's law. That is the second law of refraction. The snail's law. The sign of angle of incidence or the ratio of the sign of angle of incidence to the sign of angle of refraction is constant. Meaning sin over sin sin over sin is constant. It's constant. All right. It's constant. That is called the snail's law. That is the second law of refraction. Seen the laws that operate the lens and the mirror. Let's now look at that shortcut that you can use to know the image formed by lens and mirror. So the first thing you want to I'm going to give you an acronym. The acronym I'll be giving you is driveex. Drivex please take note of this pneumonics. Very very important. Drivex what is the meaning of driveex? Driveex. So for you to remember driveex means driver that is vexing. Is that okay? driver that is vexing. Driveex. So what has dry got to do with physics? Very simple. Drivex means for convex lens. So we are going to start with convex lens. So convex lens. Concave lens. So you are going to have to draw four. You have column, another one here, another one here, another one. Four, four column. Preferably let it be under each one. So here, now it's important to note this. Whatever is applicable for lens, the reverse is applicable for mirror. repeat, whatever applies for lens, reverse applies for mirror. When lens is converging, that mirror will be diverging. Are you there with me? So the first thing before we come to this driver, the first thing you need to take note of is this. convex lens is converging lens. So they can ask you which one is converging. convex lens is converging lens. What do mean by converging convex lens? Look at this diagram. If have this diagram, this is an example of convex lens. When light rays enters here like this. All right. Light rays enters here. Light rays enters here. The law says the light ray will move towards the wider part of this lens. So this is convex lens. Convex lens. So what part is wider? Is it this pose not pose? Is it this point or the center of the lens? You agree that for this convex is the center that is wider. So the light that enters here you remember said the lens operates by refraction. Refraction means the bending or change in direction of the light. So there will be change in the direction of this light ray towards the center which is wider. This one will move towards the center. Now what does what has happened here? Light rays that coming from different places they came and converged at this point which this is the image. So if say in school if say all SS1, SS2 and SS3 students converge in front of the principal's office at the close of school at closing time, right? It means all of you are coming from your different classes and you are meeting at point at the principal's office. All right? So that is converging. So we are converging. So this is converge. So the first thing you need to know is that convex lens converges rays. So convex lens is converging length, right? While this is concave, how do you remember concave? What is cave? cave is hole. Is hole maybe that is dug inside mountain, rock, hole that somebody can run into and hide or you can stay there. So look at this. Consider this as hole. Instead of it to be flat like this, there's hole. There's it's caved in. There is caving in here. So this is concave lens. So when you this is by concave lens. This is by convex lens. So when you have caving in that is concave. So here when light rays enters here. All right. Light ray enters here from the source. Light ray enters here. What will happen? told you the light will move towards the wider part of the lens. So what part is wider? Is it the center or the pose? You will see that the pose is wider. So this light ray that enters here it will move towards this part. This one will move towards this part. This one will move towards the wider part like that. Can you see how they move away? So that moving that scattering is what you call diverging. So concave this is concave lens. concave lens is diverging. So concave lens is diverging lens that's concave diver. So here you know told you this is where the image is formed. Where will the image be formed? Here will need to drag this back. will need to trace all these scattered rays. will trace them back. Then the point at which they meet that is where the image will be formed. Any image that is formed by tracing this back, you remember told you virtual image cannot be formed on screen. There's screen here. The image will not be formed there. So need to trace this backward for the image to be formed at the back. So any image formed by tracing back an imaginary line that image is called virtual image. It's not real image. It's virtual image. So the meaning of that convex lens will form real image while concave lens will form virtual. Now let's now go back to properties of image formed by convex lens and concave. Convex is converging. Concave is diverging. Now what is the meaning of dryx? It means for convex lens not mirror please convex lens most of the images formed by convex lens are for diminished. So most are diminished. What is the meaning of diminished? Diminished means it reduces in size. It will be smaller. means real. They are real. Real. Can you see convex lens? Real image. So they are real. Then high means they are inverted. Inverted. They are inverted. So most images. Now depending on the distance, are you with me? Depending on the distance, there could be little change here. But majorly most no matter the distance for most of them, they align with this. Therefore your concave lens the opposite of convex lens is what you have here. So the opposite of diminished is magnified. So this is magnified. The opposite of really is what? Virtual. So this is virtual image. You see virtual here. Then the opposite of inverted is erect. So or upright. Please you can write any of the two. Don't write this or this. You can write upright. You can write erect. They are the same. So these are properties of image formed by convex lens and concave lens. Now let's talk about that of mirror or mirror. You remember told you whatever is applicable for lens the reverse is applicable for mirror. So for convex mirror and concave mirror the first thing is that you see whatever is applicable for concave lens just copy it here. Whatever is here copy it here. So that means for convex mirror is opposite of what is here or just copy this here. So convex mirror is diverging is diverging mirror. Then most times the image form will be magnified. Most times virtual most time upright while for concave mirror is align the convex So it's converging image is converging is diminished most times. It is real most times and then it is inverted. Now there are few exceptions here. One of the exemptions here is that most images formed by mirror whether it's concave or convex they are usually virtual images because light cannot pass through the mirror. All right, it is thrown back. So most times they are virtual image. All right. But for the other ones, most of them are correct and you can use them in answering questions. Now, let me give you another example that you can use to practice this in your house to see whether it's correct or not. You can get spoon. Go into your kitchen. Pause this video. Go to your kitchen. Get spoon. All right? And place the spoon the inside the hole inside that spoon. That is the corn cave. Remember hole is the cave. So point that point. Okay, let me quickly do that experiment for you. Now look at this. There is power in pictures. You can easily remember what you have pictured, what you have seen. What is this? This is sponge. All right. Now, is this lens or mirror? This is mirror because it's not transparent. cannot see the other side through here. So light cannot pass through. So this is mirror. That's number one. Number two, this place that is cve caved in, this portion of this spoon that is caved in is the concave mirror. While this outside that budges out, this point that bulges out is the convex mirror. All right. So let's quickly confirm if what we are seeing here is actually true or not. Now when look at so you also have to do this experiment. If look in into this place now which is concave mirror the inside the cave can see that my head is downward and then my legs are up. So this is inverted for concave mir wrong. So let's look at it concave mirror. Can you see inverted? So this is correct. It's inverted. It's inverted. It's inverted. And then at some point as the distance is going it's getting diminished. where this diminish comes in. So as the distance gets farther, it's getting smaller and then at some distances it's the same size. But if point it out, convex mirror looking at this now my head is up. That's correct. So convex mirror my head is up upright. Convex mirror upright. So this is correct. Correct. All right. Correct. So you can also do this experiment. It will help you to remember how to answer questions online in your exams. Now having said that the last thing I'll talk about I'll talk about eye defect before leave this. So they can ask you to talk about eye defect. Number one you have myopia. Myopia is the same thing as short sight or shortsightedness. What is shortsightedness? Shortsight is the ability to see close object and not distant object. So this is what you can use to remember when you say somebody is myopic in thinking that means the person only thinks about the now. The person does not think about tomorrow. Are you with me? So if say the noise makers in this class are myopic in thinking. That means they don't think about the present. They only or they don't think about tomorrow. They only think about the present. All right? So myopia means you can only see close object. You can't see farther object. That is myopia. Ability to see close object but not distant object. How do you correct it? Before we talk about how to correct it. Now this short site the eyeball is too long or too large. Eyeball is too large. Why do they say the eyeball is too large? So let me draw how the defect how it looks like. Number one, note that your eyeball is not circle. Your eyeball is not circle. It's oval but then it has budging at the frontal part. That is how your eyeball looks like. Okay? And there is lens inside your eye. So this is the light from the source coming into this eyeball. So said the eyeball is too light. So they can ask you to draw this diagram and the corrective measure. When the eyeball is too large then it means the image forms in front of the retina. So they can draw this diagram and ask you what kind of eye defect is this? It is shortsightedness. Why this? So for short sight eyeball is too large. For long sight eyeball is too short. Are you with me? So here eyeball is too large because this is the image forming here. Normally the image is supposed to be formed on the retina. This is the retina which is the inner layer of the eyeball. So but the image forms in front of the retina. So here eyeball is too large. All right. Image form in front of retina. So how do we correct it? We need lens that can push this image. push this light ray that is converging here push it forward so that once it pushes it it can land on the retina. So what do you call that pushing light ray or that lens that has the ability to push? It is what concave or diverging length concave or diverging length. So it is corrected using concave or diverging lens. So concave or diverging lens that is introduced here will push this light ray push it further and allow it to land on the retina. While for long sight long sight is also called hyper metropia not not hyper myopia you can write that in the option. Hyperetropia hyperropia is long sight or longsightedness. What is long-sightedness? Ability to see distant object but not close object. Ability to see distant object but not close object. So longsightedness means the eyeball is too short. Because the eyeball is too short. All right. The image is from behind the retina. So here eyeball is short. Eyeball is short. image formed behind red cena. All right. So this is for short sight. This is what will happen. The image will now be formed here behind the retina. So when you see diagram like this, the eyeball is too short. This is what you call longsightedness. Longsightedness. Okay. So this longsightedness because the eyeball is too short and image is formed there. We need lens that can compress the light ray that was coming. The intensity of the light that was coming compress it before it enters this eyeball so that it will not be going farther away from the retina but it can land on the retina and that is converging or convex lens. So hyper metropia is corrected by convex or converging lines. Full stop. hope that is clear to everybody. So I'm going to stop at that point and then we go to the next topic because of our time. hope you got value. If you have gotten value on this, go to the comment section and type in driveex, type in whatever acronym or yes that you've learned from here. bought too large, bought too long, myopic in thinking, you can just type it and type value value. And let's go to the next topic. The next one I'll talk about is projectile. So for projectile they can ask you what is projectile body? projectile body is body that is launched into here that moves in parabolic shape like parabola. Okay. It's it's an object launched into here that has both vertical and horizontal components. example is bullet of gun that is shot, stone that is thrown and then tennis ball that is launched or played. Now there are four different formulas they can ask you to ask they can ask questions on and ask you to solve in part of your physics. They can ask you to to calculate time to read the maximum height time to time of flight then maximum height reach then the range. So I'll quickly give you shortcut formula you can use to know them. The first one is time to reach maximum height. Time to reach maximum height is small and that small is sin theta / sin theta / Number two time of flight. Time of flight is capital and the formula is capital is 2 sin theta / will talk about that. Number three, you have the range. The range is given as U² sin 2 theta / U² sin 2 theta / That's your rate. Your range is the horizontal distance covered. Horizontal distance covered from the point where the object was launched to where it landed. Time of flight is the time it takes the object to go up and to come down or when the time between launching it and then landing. That is the time. And the last one is the maximum height. What's the formula for maximum height? Maximum height max is giving us ² sin² theta / 2g ² sin square theta / 2g now what's the maximum height so look at this if you look at this three formula something is common there is something want to show you here you look at the time to reach maximum height how many two can you find here there is none how many two can you find here one how many two can you find here one two how many two can Find 1 2 3. So the first thing you need to note is that for these four equation there is particular formula that does not have two at all. There is one that has two occurring once. There's one that has two occurring twice. There's another one that has two occurring three times. Clock that. The next thing is this. The maximum height has the maximum amount of twos. The maximum height has the maximum amount of two which is what? 1 2 3. So two is appearing three times here and that is the maximum height. While for this one the time to reach maximum height does not have two. Now look at it your capital is two of small That's another thing to take note of. Your capital which is your time of flight is 2 * small So all they did between here and here they just added two to your sin theta / and it becomes 2 sin theta / All right. And for here this your sin 2 theta. Please take note this sin 2 theta is the same thing. Sin 2 theta is the same thing as 2 sin theta cos theta. Now of all this equation the only place where cos theta will be mentioned is range. Why? Because cos theta talks about the horizontal component. The horizontal component of force of velocity. So the only place where you have sin 2 theta in this equation is range and that sin 2 theta simply means 2 sin theta cos theta. If you this in your calculator make theta maybe 30° sin 2 * 30 that's sin 60. Then press 2 sin 30 cos 30 you will see the exactly the same thing. So range is where you have sin 2 theta. Every other place here you have 2 sin theta / u² sin 2 theta / Then here you have u^2 sin^ square theta / 2g. The meaning of sin square theta is when you find your sign of the angles. Let's say the angle is 30°. Sin 30 is 0.5. You square that 0.5. That's the meaning of sin square theta. Is that okay? Then they can ask you at what angle do need to shoot this gun to be able to get to the highest range to be able to get to the highest vertical height. You can ask you that question. You can say 30°, 45°, 90°. Now if you look at sin 30 is 0.5. So no matter what have calculated here, if multiply sin 30, no matter the amount of my sin 30 will break it down. So here if use sin 30 that's half of whatever I've calculated here but sin 90 is one sin 90 is one. So how can get 90 for here the range? Range is the horizontal distance cover. How at what degree do need to shoot my gun to be able to travel the fastest range? It is 2 * what will give me 90°? It is 2 * 45. So it's 45° because sin 2 * 45 that's 90 sin 90 is 1. All right. So if sin 90 is 1. Yeah sin 90 is one. All right. 1 * whatever have here will have the highest number. But if use sin 30 or sin 60 it will reduce the number here. Are you getting what I'm saying? The meaning of that is it is at angle 45° that the highest range will be covered. So maximum range will just be ^2 over Why is so if they say what's the formula for maximum range? Maximum range is what? U² / Why? Because this 2 * 30 will be 2 * 45 that will be sin 90. That's 1. So, ^2 / hope that is clear.