Light-reflection and refraction/CBSE/Grade-10/Physics

[00:02:18]Hello students welcome to the student the brand this is your sa now we are going to discuss about light reflection and refraction CBSC great in physics light is a form of energy which gives the sensation of sight what is that light is a form of energy which gives the sensation of sight. Well, light incident on the surface it reflect back. Okay. When light incident on the surface, it reflect back. The bouncing back of the light from the reflecting surface.

[00:02:52]The bouncing back of the light from the reflecting surface is called reflection of light. Okay. So, we'll be discussing about light.

[00:03:03]Light reflection.

[00:03:08]reflection and a refraction, light reflection and a refraction.

[00:03:21]Well, light incident on the surface normally uh there are different types of surfaces like a plain surface, like a regular surface, irregular surface, different types of surfaces are there.

[00:03:36]So we will discuss about those uh surfaces uh after this topic after completion of light reflection. So we'll discuss about surfaces. We'll see here.

[00:03:47]So I'm taking here this is a plain surface.

[00:03:52]This is a plain surface. When the light is incidenting on it this incident ray incident ray the lighter which is incidenting on the surface is called incident ray. The light ray which is reflecting back is called reflected ray.

[00:04:09]So I'm considering here incident ray incident ray and I'm considering here this reflected ray reflected ray and the light ray which is perpendicular to the plane surface is called normal line normal.

[00:04:32]Okay. So the lighter which is incidenting on it is called incident ray. The lighter which is reflecting back is called reflected ray. Here you can observe incident ray reflected ray normal line incident ray reflected ray normal line.

[00:04:52]And here I'm considering the uh deviate undeated line undeated line and the angle between incident r and normal line is called angle of incidence. Angle between reflected and normal line is called angle of reflection. Angle between reflected ray and univered line is called angle of deviation.

[00:05:18]angle of deviation. Okay. So the bouncing back of the light from the reflecting surface the bouncing back of the light from the reflecting surface is called reflection of light. So the angle between incident ral is called angle of incidence. Angle between reflected and normal line is called angle of reflection. Angle between reflected ray and dev line is called angle of deviation. Yes, I hope it is very clear now. So I can see loss of reflection, loss of reflection.

[00:06:04]Okay, what are the loss of reflection?

[00:06:06]Point number one.

[00:06:08]So incident ray, reflected ray normal lies on the same plane. Incident reflector normal lies on the same plane.

[00:06:18]Okay. Angle of incidence is equal to angle of reflection.

[00:06:23]Angle of incidence is equal to angle of reflection. So this is about reflection of light and loss of reflection.

[00:06:32]Reflection of light.

[00:06:39]reflection of light.

[00:06:44]Okay. So, incident reflected and normal line angle between incident and normal line is called angle of incidence. Angle between reflected and normal line is called angle of reflection. Angle between reflector and dev is called angle of deviation. So loss of reflection incident reflected and normal line lies on the same plane. Angle of incidence is equal to angle of reflections. I hope it is very clear understood or not now. So we'll discuss about one more point that is angle of deviation. Shall we take out angle of deviation? Angle of incidence plus angle of reflection plus angle of deviation equal to 180°. Because this is a linear angle, right? 180° linear angle. So we can also represent pi radians. Okay.

[00:07:46]180° right? So here you can observe here I'm taking from loss of reflection angle of incidence is equal to angle of reflection. Right? So we can substitute here angle of incidence plus angle of incidence plus angle of deviation equal to 180°.

[00:08:10]angle of deviation = 180 minus 2 angle of incidence angle of deviation = 180 minus to angle of reflection okay so very very important formula very very essential formula so angle of deviation equal to 180 minus two angle of incidence angle of deviation equal to 180 minus 2 angle of reflection so I hope it is very clear Right.

[00:08:45]Okay.

[00:08:47]Thank you.

[00:08:50]So here you can observe. So this about uh reflection of light, loss of reflection and angle of deviation formula. So I hope it is very clear. So now we'll discuss about so regular reflection and irregular reflection.

[00:09:34]regular reflection and irregular reflection. So coming to regular reflection, regular reflection, regular reflection.

[00:09:49]So I'm taking here plain surface. I'm considering the plain surface. So this is a plain surface.

[00:10:00]So incident light are parallel.

[00:10:04]So these light rays are parall to each other.

[00:10:10]Then I'm taking the reflector light.

[00:10:12]These are the reflector light rays.

[00:10:21]So incident beam, incident parallel beam, incident parallel beam, reflected parallel beam.

[00:10:41]So smooth surface Smooth surface, regular reflection.

[00:10:52]Coming to irregular reflection.

[00:11:24]So here you can observe reflection is taking place on smooth surface. Here reflection taking place on rough surface because incident lighters are parall but reflector lighters are not parall to each other. Right.

[00:11:40]Incident lighters are parallel.

[00:12:05]So incident light rays are parallel but reflector light rays are not parallel to each other. This type of reflection is called irregular reflection also known as diffuser reflection. Okay. So regular reflection it takes place on smooth surface. Incident parall beam reflector parall beam. Here incident lighters are par but reflector lighters are not parall to each other. This type of reflection is called irregular reflection or diffuser reflection. Okay.

[00:12:33]So coming to the next one. So till now we discussed about plane mirror.

[00:12:40]So object So now you can observe.

[00:13:10]So till now we discussed about plane mirror about plane mirror like when light incident on it after reflection it bounces back the phenomena bouncing back of the light from the reflecting surface is called reflection of light. Uh simply we can say uh when light is incident on the surface it reflect back uh getting reflected into the same medium that is known as reflection of light. Okay. And the next point is regular reflection and irregular reflection. In regular reflection if you observe carefully incident lighters are parallel then reflector lighters are also parallel to each other. Okay. Incident lighters are parallel. Then reflector lighters are also parallel to each other. Here parallel beam is incidenting on it after reflection. So the reflected beam also parallel. Okay. So and coming to irregular reflection are also known as diffused reflection. So why we are calling it is irregular reflection or diffuser reflection means incident lighters are parallel but reflector lighters are not parallel to each other.

[00:14:14]Incident lighters are parallel but reflector lighters are not parallel to each other. I hope it is very clear. So that type of reflection is called irregular reflection or diffuser reflection. I hope it is very clear.

[00:14:26]Next one we'll be talking about mirrors.

[00:14:30]Okay. So mirrors only uh still two more points are left after completion of that we'll discuss about spherical mirrors.

[00:14:38]So in mirror object and image. So what is object? What is image? After that nature of the image formed by the plane mirror we'll discuss right. So I'm taking here this is the plane mirror. This is a plane mirror. Understood or not? So I'm considering here light rays are coming from uh some from the from the source after reflection those light rays are meeting at one point after. So this is the real real object real image real image. Okay. So if you observe carefully here what is happening here? So if you observe these are the reflected light rays right I1 I2. So this is about I1 R1 and I2 R2. So this is about real image.

[00:15:28]What do you mean by real image? After reflection all light are meeting at one point. After reflection all light rays are meeting at one point on the principal axis. That is called real image. Directly reflect the light. So if you observe one thing directly reflect light are meeting if directly reflect light are meeting that image is called real image. If you are extending the incident light rays extended incident light rays are meeting at one point that is a virtual object.

[00:16:00]Okay. So reflector light are meeting at one point that is a real image. Extended incident lighters are meeting at one point that is a virtual object. Okay.

[00:16:10]And one more I'm taking here. So this is this is all about plane mirror and object and image. So here I'm taking the point object. Real object. So point object that to real object I'm taking means like a candle torch light uh like this type of examples we can say right.

[00:16:33]So from this point light rays are coming. From that point light rays are coming. So I'm taking here this is the point source. So from the point source light rays are coming after reflection what happens those reflector light rays are extended extended reflector lighters. If you observe carefully I1 R1 and this is about I2 R2. So I hope it is very clear. So we are extending the reflector lightness extended reflector light are meeting at one point. So if you observe carefully extended reflector light rays R1 R2 extended reflector light rays are meeting at one point their image is forming that is a virtual image so I hope it is very clear do you understand or not do you are you understanding are you understanding or not okay so here you can observe so now I'm taking like this object and image object and image So object is real. Image is virtual. Object is virtual. Image is real. Object is real. Image is virtual. Object is virtual. Image is real. I hope it is very clear. Right? Yes. So just check once. So light rays are coming from infinity. After reflection those light rays are meeting at one point their image is forming. What type of image is forming? Real image. And we are extending the incident light. Extended incident light are meeting at one point their image is for that's not image so object we are extending the incident light extended incident light are meeting at one point that point is virtual object and here you can see I'm taking the point object from the point object lighters are coming after reflection those extended reflector lighters are meeting at one point extended reflector lighters are hitting at one point there image is forming that image is called virtual image. That image is called virtual image. I hope it is very clear understood or not? Yes. So object is real. If object is real, image is virtual. If object is virtual, image is real. Vice versa, object is real, image is virtual, object is virtual, image is real. Right? Yes. So that's about this diagram. Now we'll discuss about nature of the image formed by the plane mirror. Nature of the image nature of the image formed by the plane mirror. So I'm taking here So this is the object AB.

[00:19:37]So one lighter I'm taking like this after reflection. So actually when the light ray is passing along the normal line if the light ray is passing along the normal line it retrace its original path. If the light ray is passing along the normal line it retrace its original path. Okay. So that is very very important that uh this concept we are using here why light ray is passing okay along the normal light it reflect back here also I'm taking here so I can observe after reflection here also I'm taking one more understood or not Yes.

[00:20:37]So, a dash and b dash.

[00:20:40]So, this the height of the object and the height of the image.

[00:20:48]And this is object distance.

[00:20:51]And this one is the image distance.

[00:20:55]Object distance. Image distance. Height of the object and height of the image. I hope it is very clear. Understood or not? Point number one. Point number one.

[00:21:05]If object is real, image is virtual.

[00:21:09]So I'll write C just now explain a table column like object is real image is virtual if the object is real image is virtual object is virtual image is real likewise here also we will discuss point number one object is real image is virtual object is virtual image is real coming to the point number two object distance is equal to image distance object distance is equal to image distance and the third one height of the object is equal to height of the image.

[00:21:46]So this height you are taking right this height of the object is equal to height of the image. And coming to the fourth one nature of the image is virtual. So we can take magnification is + one.

[00:21:59]Magnification of the plane mirror is + one. Why sir? Why it is + one? Why can't we take remaining numbers? There are numbers so many are there. So why you are taking only one that to plus one because object and image will be same that to virtual and erect above the principal axis the image will form virtual and erect. So virtual image will be getting positive sign right. Yes. So here object by image. So we can take both are equal. If you are mentioning one means both are equal that two positive means so one is virtual image.

[00:22:35]Okay. Now coming to the fifth one.

[00:22:40]So it also shows lateral inversion. So lateral inversion.

[00:22:48]Lateral inversion.

[00:22:51]Lateral inversion.

[00:22:54]Lateral inversion. So what do you mean by lateral inversion? So if you go and stand in front of the plane mirror and lift your right hand, it appears in the left side. If you lift your left hand, it appears in the If you lift your right hand, it appears in the left side. If you lift your left hand, it appears in the right side.

[00:23:16]Okay. This mirror image, this converting of right side of the object appears to be left side of the image. Left side of the object appears to be right side of the image. Mean this mirror image is called lateral inversion. This mirror image is called lateral inversion. So I hope it is very clear. Understood or not? Yes. So yes here you can see lateral inversion. So point number one object is real image is virtual object is virtual image is real. Object distance is equal to image distance when you are coming to the plane mirror where the object is placed in front of the mirror. So same size of the image is forming that time object distance is equal to image distance and height of the object is equal to height of the image and magnification is + one and lateral inversion. So what do you mean by lateral inversion? So did you observe? So ambulance is coming back of us. The letters written on the ambulance will be in the form of mirror image.

[00:24:09]When you see in the radio mirror that is side mirror of the car, a bike okay or bus if you see uh the letters written on the amance will appear very clear like am normal format because so the letters whatever it is there it is in the format of late uh like a lateral inversion like a mirror image. Okay. So I hope it is very clear. So that's enough about uh nature of the image formed by the plane mirror. Coming to the next one.

[00:24:44][singing] La [singing] one camera and convex mirror. I'll discuss about mirrors. That's enough. So for today class until mirrors we'll discuss. Then uh we'll go for next class with the lens. Okay. So here I'm taking the concave mirror.

[00:25:32]Concave mirror. The mirror which is in the form of spherical shape. So if you are taking the sphere this we are taking the small portion. We taking small portion right? We are not taking entire portion. We are taking a small portion.

[00:25:45]Is it clear or not? So that small portion based on reflection of light here if you're taking reflection takes place inward reflection takes place inward that is called concave mirror. So whereas here reflection takes place outward. So if you observe here this mirror which is uh okay which is bulged outward. So here bulge inverse means the reflection takes place inward that is called concave mirror and also known as concirror is also called converging mirror. Sir why you are calling it as a converging mirror? Do you have any specific reason? All right. So do you have any valid reason for that? Yes of course we have that. Right. So that is when light rays are incidenting on it after reflection those light rays are moving towards the principal axis. So what mirror is doing? Converging the light rays. What mirror is doing?

[00:26:46]Converging the light rays in which direction converging towards the principal axis where the light rays are meeting at the principal axis at one point. That point is called focus.

[00:26:58]Yes, there are many points when you are going to the uh concerts in depth. We are discussing about pole, focus, center, curvature. We will discuss about all the points. Now we are discussing about concave mirror, convex mirror, nature of concave mirror, nature of convex mirror where light rays are inserting on it. After reflection, those light rays are meeting at one point on the principal axis. Concave mirror is converging all lighters towards the principal axis.

[00:27:25]After reflection, the lighters are meeting at one point. that point is called focus.

[00:27:30]So coming to the convex mirror after reflection those lighters are moving away from the principal axis. So after reflection those lighters are moving away from the principal axis that's why it is called diverging mirror diverging mirror so I hope it is very clear now coming to the next one.

[00:28:06]So now we are discussing about uh terms we'll discuss for today class we'll discuss about terms. So still so many points are there.

[00:28:16]So because of time limit we are talking about only terms related to specula.

[00:28:25]What are those terms? Terms terms or nomicature terms are nomomenclature. So I'm taking the concave mirror actually it is a part of this sphere. So particularly I'm taking concave mirror.

[00:28:40]Okay. So we can take convex mirror also.

[00:28:43]Sir why only you are taking concave mirror? Why can't we take convex mirror sir? Why can't we take do you have any like specific reason to take that? No, not like that. So we can take convex mirror also. We are taking spherical mirror. So we need to understand in detail. So that is the reason for specific point of view for clarity we are taking concave mirror. Right? So it is a part of the sphere. We know that anyway it is a part of the sphere. The center of the imaginary sphere in which mirror is a part. Midpoint of the mirror is called pole. Midpoint of the mirror is called pole. The line joining of center curvature and pole is called principal axis.

[00:29:28]Line joining of principal axis. Line joining of center curvature and pole is called principal axis. So the distance between center curvature and pole is called radius of curvature. The distance between central curvature and pole is called radius of cvature. [singing] Radius of cvature.

[00:29:48]Radius of curvature.

[00:29:52]So after reflection all are meeting at one point.

[00:30:01][singing] Okay. A soft reflection all are meeting at one point that point is called focus.

[00:30:11]I hope it is very clear. The distance between center curvature to pull is called radius of curvature. The distance between focus to pole is called focal length. Focal length. So I hope it is very clear understood. So once again discuss all the points. Center curvature, pole, principal axis, radius of curvature, focal length and sixth one is uh actually this is a focus focal length and coming to the seventh one apart the width of the width of the reflecting surface where reflection of light taking place that is called reflection of light. Understood or not? uh sorry uh aparture reflection of light taking place that part is called aparture. I hope it is very clear until this so thank you so much for joining attending and listening so giving an opportunity if you like the content if you like the channel do like share and subscribe to student brand.

[00:31:08]Thank you so much we'll see you in the next class. Thank you.