Ray Optics/Grade-12/JEE/NEET/Physics

Added: 2026-05-27

[00:01:14]Hello students.

[00:01:27]Hello students. Welcome to the student the brand. This is today we are going to discuss about ray optics grade 12 topic.

[00:01:41]Okay.

[00:01:43]So here all the points related to spherical mirrors and plane mirror. After that we will discuss about lenses.

[00:01:56]After that we will discuss about I defects right.

[00:02:02]So these are all we are going to discuss.

[00:02:07]Okay.

[00:02:08]So let's start the topic.

[00:02:13]Light is a form of energy.

[00:02:16]Light is a form of energy which gives the sensation of sight.

[00:02:22]Light is a form of energy which gives the sensation of sight. When light is incidenting on the surface, it bounces back or reach to our eyes then only we can able to see the object.

[00:02:40]Okay. And here so in our topic we will consider light as a ray ray optics the branch of physics which deals with the properties of light okay when it is incidenting and when the light is refracting okay how it will be reacting and the characteristics of the light okay and next Here we will discuss about luminous object, non- luminous object.

[00:03:17]Luminous object and a non- luminous object. So what is the meaning of luminous object?

[00:03:27]The object which emit their own light.

[00:03:32]The objects which emit their own light those are called luminous object. So example for luminous object.

[00:03:42]So sun glowworm.

[00:03:46]Okay. So these are all example for luminous object. Coming to non luminous object. The object which does not give their own light but reflect the light rays.

[00:04:02]But they reflect the light rays when it is falling on them. Example for non- luminous objects uh we can take a sun sorry earth wall.

[00:04:16]So when lightless incident on it reflect back okay and so these are on non luminous objects.

[00:04:29]So coming to the ray and beam.

[00:04:34]So how can you differentiate? So if you're taking single light ray that is called ray of light. Single light ray.

[00:04:42]If you are taking ray.

[00:04:46]So if you're taking number of light rays together that is called beam.

[00:04:53]Number of light rays together that is called beam.

[00:04:57]beam of light.

[00:05:00]So single ray is considered ray of light. Number of rays together that is called beam of light. Okay. So our topic is ray of light.

[00:05:14]Ray optics.

[00:05:18]Re optics.

[00:05:37]Okay.

[00:05:39]So yes, now when light is incidenting on the surface, I'm taking this the plane mirror.

[00:05:49]This is the plane mirror.

[00:05:53]Plain mirror. Highly polished smooth surface.

[00:05:59]Highly polished smooth surface.

[00:06:03]Okay. When light is incidenting on it, reflect back. When light is incidenting on it, reflect back. The bouncing back of the light from the reflecting surface is called reflection of light. So I'm taking the incident ray.

[00:06:19]Reflected ray.

[00:06:21]And the light ray which is perpendicular to the plane surface is called normal line. Once again incident ray reflected normal light. Okay. The light ray which is incidenting on it is called incident ray.

[00:06:37]Incident ray. The light ray which is reflecting back is called reflected ray.

[00:06:45]Reflected ray. And this one I'm considering the normal normal the light which is actually it is not existed normal line is not existed for better understanding of reflection of light reflection phenomena we are drawing the dotted line okay so now we can take here so the angle between incident and normal is called angle of incidence Angle between refracted ray normal line is called angle of refraction. Angle between reflected and undeated line or initial direction of the incident ray is called angle of deviation.

[00:07:33]Once again incident reflected normal line. So this is the unde line or initial direction of the incident ray. Angle between incident and normal line is called angle of incidence. Angle between reflected and normal line is called angle of reflection. Angle between reflected and deviated line is called angle of deviation.

[00:07:54]Okay. So I hope it is very clear. So this is the plane mirror smooth surface smooth surface and one more you can see the angle between incident and plane surface is called glancing angle of incidence.

[00:08:13]Angle between reflected ray and plane surface is called glancing angle of reflection.

[00:08:19]Glancing angle of reflection. Angle between incident and plane surface is called glancing angle of incidence.

[00:08:28]Angle between reflected and plane surface is called glancing angle of reflection.

[00:08:33]Understood or not? I hope it is very clear. Now you can see here. So loss of reflection coming to loss of reflection.

[00:08:49]So those are first point is incident reflected normal line incident reflected a normal line lies on the same plane.

[00:09:00]And coming to the point number two angle of incidence is equal to angle of reflection.

[00:09:07]And so these two points are very very important. One is incident reflected normal line lies on the same plane.

[00:09:17]Incident loss of reflection. Incident ray reflected a normal line lies on the same plane at same the point of incidence. Okay. So angle of incident is equal to angle of reflection. Angle of incidence is equal to angle of reflection. Understood or not? Angle of incidence is equal to angle of reflection. So I hope it is very clear right. So next angle of deviation formula.

[00:09:46]So you can see angle of deviation equal to in sorry right from starting onwards we'll discuss then you'll get angle of deviation the angle of angle of deviation angle of deviation equal to.

[00:10:18]So angle of incidence plus angle of reflection plus angle of deviation equal to 180° linear angle. Understood or not? So here you can see angle of incidence plus angle of reflection plus angle of deviation equal to total 180°.

[00:10:38]Okay, linear angle. Is it clear or not?

[00:10:41]So now you can see from loss of reflection from loss of reflection angle of incidence is equal to angle of reflection from loss of reflection angle of incidence is equal to angle of reflection. So angle of incidence plus angle of incidence plus angle of deviation equal to 180°. So angle of deviation equal to 180 minus 2 angle of incidence angle of deviation equal to 180 minus 2 angle of reflection.

[00:11:16]Understood or not? So this is very very important. So instead of angle of reflection if I substituting angle of incidence I'm getting angle of deviation formula 180 minus 180 minus so angle of deviation equal to 180 minus 2 angle of incidence and if you're taking angle of deviation equal to 180 minus 2 angle of reflection to angle of reflection understood or not so this about angle of deviation This is about angle of deviation.

[00:11:54]Yes. So next Okay. So now we will discuss about regular reflection and irregular reflection. Now I'll discuss about regular reflection and irregular reflection. So I'm taking the plane surface here. This is the plane surface.

[00:13:09]So inside are parall to each other. So like this you can take here also and here also you can take. So incident par beam and here you can see if you see so normally this is a parall beam.

[00:13:36]This is a parallel beam.

[00:13:39]Okay. All light rays are parall to each other. So this is a convergent beam.

[00:13:47]Convergent beam all light rays are converging to one point. So whereas diverging beam like this light rays are moving away from one point.

[00:14:04]So this the parallel beam.

[00:14:09]Parallel beam.

[00:14:12]So convergent beam.

[00:14:19]Convergent beam.

[00:14:23]Convergent beam of light. Parallel beam of light. And divergent beam of light.

[00:14:30]Divergent.

[00:14:33]divergent understood or not? So here if you observe carefully if you observe carefully so these light rays are parallel to each other. Light rays are parall to each other. So parall beam of light and here so the light rays are coming to one point. Okay. So getting closer converging to one point. So that's why convergent beam whereas here from one point the light rays are moving okay so moving in different directions moving in different direction so that is a divergent beam understood or not convergent beam or divergent beam so I hope it is very clear convergent beam of light rays divergent beam of light rays okay so here the light rays which are incidenting on it. Those are parallel to each other.

[00:15:34]That's why incident parallel beam of light. Okay. Incident parallel beam of light. Incident parallel beam.

[00:15:50]Incident parall beam. And coming to your after reflection though light rays are moving away from it here.

[00:16:03]Okay. Reflected parallel beam.

[00:16:08]Reflected.

[00:16:12]Reflected parallel beam.

[00:16:16]Understood or not? So this is about regular reflection.

[00:16:20]Regular reflection.

[00:16:24]Regular reflection.

[00:16:29]So it is taking place on smooth surface.

[00:16:36]So example plane mirror.

[00:16:44]So on plane mirror regular reflection of light takes place coming to irregular reflection.

[00:16:52]So this a regular reflection.

[00:16:56]Regular reflection of light.

[00:17:01]Regular reflection of light. Coming to irregular reflection. So here you can see irregular reflection.

[00:17:12]Irregular reflection.

[00:17:21]So surface is not smooth.

[00:17:25]surface is rough.

[00:17:28]So rough surface I'm taking here.

[00:17:31]This a rough surface.

[00:17:44]Okay. Incident light rays are parallel but reflector light rays are not parallel to each other. Incident light rays are parallel but reflect light rays are not parallel to each other. So this is about irregular reflection. So here you can observe Incident light rays are par but uh reflect light rays are moving in different directions.

[00:18:34]So incident parall beam.

[00:18:40]So incident light race I'm taking incident light and reflect light rays reflect light rays understood or not. So incident light rays are par but reflect light rays are not par to each other. So this about irregular reflection. Irregular reflection takes place example on rough surface surface is rough.

[00:19:16]Example wall.

[00:19:24]Okay.

[00:19:26]A rough surface it takes place. Is it clear or not? Once again observe all the points.

[00:19:34]So just check once.

[00:19:59]Understood or not?

[00:20:12]So coming to the next one object and image.

[00:20:27]object and image.

[00:21:05]So now we'll discuss about object elements here plane mirror.

[00:21:16]So optic center sorry this is about when light rays are coming from infinity our source after reflection those light rays are meeting at one point this is a real image real image understood or not if you're extending the light rays those light rays are meeting at one point.

[00:21:46]So this is the virtual object.

[00:21:50]Virtual object understood or not? So here light rays are coming from the source. After reflection those light rays are meeting at one point. So here this is the real image where extending the incident light rays. Extended incident light rays are meeting at one point that is virtual object. Okay. So coming to the next one.

[00:22:15]So from the point real object from the point light rays are moving away from it.

[00:22:27]After reflection those light rays are meeting here. This is a virtual image.

[00:22:34]Virtual image. Understood or not? This is a virtual image.

[00:22:39]Okay. So observe carefully the point of intersection of reflector light rays directly reflect light rays are meeting at one point that's why that is called real limit. So we are extending the incident light rays extended incident light are meeting at one point that is a virtual object and here you can see from the point light are coming after reflection we are extending the reflector light extended reflector light rays are meeting at one point there virtual image there virtual image I hope it is very clear so by observing this point we can conclude that so I'm concluding like this that is Object and image. Object is real. Image is virtual. Object is virtual. Image is real. Okay. Object is real. Image is virtual. Object is virtual. Image is real. Vice versa. If the object is virtual, image is real. If the image is real, object is virtual. Okay. So, I hope it is very clear. Understood or not? So, coming to the next one.

[00:23:47]Next one we will discuss about nature of the image formed by the plane mirror.

[00:23:57]Nature of the image formed by the plane mirror. So see so here I'm taking the plane mirror.

[00:24:07]This is the plane mirror.

[00:24:27]So observe carefully this object height of the object height of the object.

[00:24:39]Okay. Okay. So when the light ray is passing along the normal line, when the light ray is passing along the normal line, what happens? It reflect back or retrace its original path. So here also I'm taking like this.

[00:24:54]Understood. How many light rays are required to form the image of the object? Number of light rays are required to form the image of the object. Minimum two. Minimum two light rays are required to form the image of the object. Minimum two light rays are required to form the image of the object. Understood or not? So I'm taking one lighter here after reflection and one more lighter here. After reflection those are moving away from it.

[00:25:26]So height of the object is zab and here we are extending.

[00:25:39]So a dash b dash a dash and b dash okay image. So here you can see so this one is called height of the object and this one is the height of the image and here I'm taking the object distance and here if you are considering the image distance okay so these are all points first point is just I discussed if object is real image is virtual object is virtual image is real. Coming to the second point object distance is equal to image distance. Okay. So object distance is equal to image distance. Coming to the third one height of the object is equal to height of the image. Height of the object is equal to height of the image.

[00:26:45]Understood or not? And coming to the next one, magnification of the plane mirror is + one. Magnification of the plane mirror is + one. Coming to the fifth one, it also shows lateral inversion. It also shows lateral inversion. So what is what is the meaning of lateral inversion?

[00:27:09]Lateral inversion is nothing but the phenomena of 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.

[00:27:21]This mirror image is called lateral inversion. Lateral inversion once again.

[00:27:27]So if you stand in front of the plane mirror, our right side object appears to be left side of the image. Our left side of the object appears to be right side of the image. This mirror image is called lateral inversion. Lateral inversion. Understood or not? So I hope it is very clear. Just check once. If the object is real, image is virtual. If the object is virtual, image is real.

[00:27:50]Object distance is equal to image distance. Height of the object is equal to height of the image. So magnification is + one. And here one more point. So plane of mirror forms virtual image virtual and same size virtual and same size okay plane mirror forms virtual and same size that's why magnification of the plane mirror is + one that's why magnification of the plane mirror is + one understood or not so I hope it is very clear so coming to the next one. So we'll discuss we'll discuss number of images number of images.

[00:28:40]So actually this is the plane mirror whatever I'm taking this is a plane mirror. Now if two plane mirrors are inclined, if two plane mirrors are placed inclined at an angle if two plane mirrors. So these are the two plane mirrors like this.

[00:29:16]So angle between two plane mirrors is theta.

[00:29:29]Okay. So n = 360 by theta -1.

[00:29:37]Okay. N is the number of images formed by the plane mirrors. Number of images.

[00:29:43]So if you are inclined at any angle theta okay so number of images formed by the two plane mirrors is so 360 by theta if if 360 by theta is even okay understood if it is odd so we have to take 360 by theta only.

[00:30:10]So if it is odd we have to take 360 by theta.

[00:30:15]Understood or not? So I hope it is very clear.

[00:30:20]Shall we take one example? I'll give an example then you'll get to know. I'll give an example. So I'm taking theta = theta.

[00:30:39]Shall we take 30°?

[00:30:44]Theta is 30°.

[00:30:46]Then n = theta = 30° n = 360 by theta.

[00:30:52]So theta 0 0 get cancel 3 1 3 2. So n is the even number I know n is the even number. So that's why then n = 12 - 1 that is 11. number of images formed by the plane mirror is 11.

[00:31:13]Okay. So here if it is odd number comes like 9 7 5 then you have to keep it like this. Okay. But when it comes to even you have to remove minus one. So I hope it is very clear. So number of images formed by the plane mirror. Two plane mirrors when they are inclined at an angle theta.

[00:31:46]So I hope it is very clear understood or not. So coming to the next one.

[00:31:54]Till now we discussed about plane mirrors.

[00:31:59]Till now we discussed about plane mirrors. Now we are going to discuss about spherical mirrors. The mirror which is in the form of curved surface. The mirror which is in the form of curved surface. So I'm taking here this a curved surface.

[00:32:18]So actually there are two mirrors are there. Spherical mirror. One is concave mirror.

[00:32:26]concave mirror and the second one is convex mirror.

[00:32:36]So convex mirror concave mirror and convex mirror is it clear or not? So concave mirror is also known as converging mirror whereas convex mirror is also known as diverging mirror. So here you can see when our light rays are incidenting on it after reflection those light rays are moving towards the principal axis.

[00:33:05]Okay. So after reflection light rays are moving towards the principal axis that's why it is converging whereas diverging.

[00:33:14]So when light rays are incidenting on it those light rays are moving away from it like this. So if you're extending this reflector light rays those reflector light rays are meeting at one point extended reflector light rays are meeting at one point. Is it clear or not? Okay. So just check once spherical mirrors concave mirror and convex mirror concave mirror and convex mirror.

[00:33:49]So concave mirror is also known as converging mirror whereas convex mirror is also known as diverging mirror. Is it clear or not?

[00:33:59]Yes. So now we'll discuss about terms related to spherical mirror.

[00:34:05]Terms related to spherical mirror. Let's discuss about it.

[00:34:26]terms related to spherical mirror.

[00:34:33]So it is a part of the sphere center of the imaginary sphere. First one is center of curvature.

[00:34:42]So concave mirror I'm taking.

[00:34:45]So the midpoint of the mirror is called pole.

[00:34:49]Center of the imaginary sphere.

[00:34:52]Center of the imaginary sphere in which mirror is a part is called central curvature. And midpoint of the mirror is called pole. And the line joining of center curvature and pole is called principal axis.

[00:35:11]principal axis.

[00:35:14]And coming to the fourth one, the distance between central curvature to pole is called radius of curvature.

[00:35:22]The distance between central curvature to pole is called radius curvature r.

[00:35:30]And coming to the fifth one after reflection all light rays are meeting at one point. So I'm taking here all light rays after reflection.

[00:35:42]light rays are meeting at one point here. You can observe there is a focus capital F. So the distance between focus to pole is called focal length.

[00:35:54]And coming to the second one, width of the reflecting surface is called aperture.

[00:36:00]So this reflecting surface is called aperture.

[00:36:08]Understood or not? So these are terms related to spherical mirror.

[00:36:14]These are terms related to spherical mirror. Just check once.

[00:36:19]So central curvature pole principal axis.

[00:36:30]Okay.

[00:36:53]So I hope it is very clear.

[00:36:56]So understood or not? So these are terms related to spherical mirror. So next one we will discuss about ray rules.

[00:37:10]Ray rules ray rules of concave mirror and rules of convex mirror.

[00:37:33]So I'll discuss about rules of concave mirror and rules of convex mirror. So conc.

[00:37:42]So pole focus center curvature light ray is coming from infinity after reflection passes through focus.

[00:37:53]Coming to the second one.

[00:37:58]So pole focus center curvature light ray passing through focus after reflection most towards infinity.

[00:38:10]Coming to the fourth one third one pole focus center curvature light rays passing through center curvature.

[00:38:23]Light ray is passing through center curvature. It reflect back into the same path. And coming to the fourth one.

[00:38:33]Coming to the fourth one here you can see.

[00:38:36]So pole focus center curvature.

[00:38:42]Light ray is incidenting at the pole after reflection.

[00:38:47]So these are arrows. One. Check here.

[00:38:52]These are railroads.

[00:39:08]Understood or not?

[00:39:17]Ray rules of concave mirror. Coming to the ray rules of convex mirror. So now you can see convex mirror.

[00:39:31]So poor focus central curvature light ray is coming from infinity.

[00:39:40]After reflection passes through focus.

[00:39:46]After reflection passes through focus.

[00:39:50]Coming to the second one here you can observe.

[00:39:58]So pole focus center curvature light ray is passing through focus after reflection moves towards infinity.

[00:40:12]Lighter is reflecting. Okay. Lighter is passing through focus after reflection moves towards infinity. And coming to the third one here you can observe.

[00:40:23]So pole focus center curvature.

[00:40:28]Light ray is passing through center curvature.

[00:40:33]Light ray is passing through center curvature. After reflection it is its original path. Coming to the fourth one.

[00:40:43]So here po focus center curvature light incident at the pole it reflect back.

[00:40:56]Okay so just check once check once here.

[00:41:03]So these are the rules of concave mirror and convex mirror. Ray rules of concave mirror and convex mirror. Next we will discuss about image formation.

[00:41:16]Image formation by concave mirror and convex mirror.

[00:41:22]Image formation by concave mirror and convex mirror. So let's discuss about it.

[00:41:29]Let's discuss about it.

[00:42:18]so image formation by concave mirror and image formation by convex mirror we will discuss. So here I'm taking the concave mirror.

[00:42:29]So light rays are coming from infinity.

[00:42:33]So pole focus center curvature. Pole focus and center curvature.

[00:42:42]So object is placed at infinity.

[00:42:47]Object is placed at infinity. One light I'm taking like this. Another light I am taking like this. After reflection here image is forming at focus. Nature of the image is real and inverted. Size of the image is highly diminished. Point number one.

[00:43:08]Size of the image is highly diminished.

[00:43:11]Object is placed at infinity. Image is formed at focus. Nature of the image is real and inverted. Size of the image is highly diminished. Coming to the next one.

[00:43:28]So pole focus center curvature object is placed.

[00:43:38]One lighter I'm taking like this another lighter is passing through focus.

[00:43:46]The image will form between C and F.

[00:43:50]Image will form between C and F.

[00:43:52]Understood or not? So object is placed beyond C.

[00:43:58]Beyond C. Image is forming between C and F. Nature of the image is real and inverted. Size of the image is diminished.

[00:44:12]Size of the image is diminished compared to the object.

[00:44:16]Yes. So coming to the third one.

[00:44:27]So pole pole focus center curvature light is in object is placed at C image also will form at C. One light I'm taking it passes through focus. Another light is inside the pole.

[00:44:51]No lighters are here.

[00:44:59]Object is at C. Image is at C. Nature of the image is real and inverted. Size of the image is same size.

[00:45:12]size of the image is same size.

[00:45:14]Understood or not? So these are image formation by concave mirror. Image formation by concave mirror. So next we will discuss about so three more cases in concave mirror.

[00:45:31]Three more cases.

[00:45:48]Okay, three more cases of conc. Let's discuss about it.

[00:46:31]So here fourth one so pole focus center curvature object is placed between C and F light I'm taking like this it passes through focus another light in the pole it reflect back.

[00:46:59]Oh, object is placed between C and F.

[00:47:18]Object is placed between C and F. Image will form behind C.

[00:47:27]Beyond C nature of the image is real and inverted size of the image is enlarged.

[00:47:37]Size of the image is enlarged.

[00:47:39]Understood or not? And coming to the fifth one.

[00:47:48]So pole focus center curvature object is placed at F.

[00:48:00]One light I'm taking another light will be so object is at f image will form at infinity nature of the image is real and inverted size of the image is highly enlarge nature of the image is real and inverted. size of the image is highly enlarged. Okay. So coming to the next one concave mirror.

[00:48:40]So sixth case so pole focus central curvature so object is placed between f and p one light I'm taking like this okay so it is passing through focus is another light incident at the pole. It reflect back.

[00:49:16]Okay. Object is placed between F and P.

[00:49:21]Image is formed behind the mirror.

[00:49:30]Here the image will form.

[00:49:34]Object is placed between F and P. image will form behind the mirror. Nature of the image is virtual and erect. Size of the image is enlarged.

[00:49:46]Size of the image is enlarge compared to the object. Image size is increased.

[00:49:52]Okay. So coming to the next one convex mirror.

[00:50:15]So I'm taking the convex mirror is like this.

[00:50:19]So for focus center curvature object is placed at infinity one light I'm taking like this so the light rays are meeting at f object is at infinity image is forming at f nature of the image is virtual and erect nature of the image is virtual erect and highly diminished Virtual and highly diminished.

[00:50:51]Understood or not? Point size image is formed at focus point size images forming at focus. So coming to the next one two more one more case for convex mirror.

[00:51:06]So I'm taking like this.

[00:51:09]So this is the pole focus center curvature object is placed between P and infinity light I'm taking like this after reflection passes through focus after reflection passes through focus another light ray so here you can observe these light rays are meeting between P and F object between P and infinity images forming between P and F.

[00:51:43]P and F nature of the image is nature of the image is virtual erect and diminished compared to the object image size is decreased. Compared to the object image size is decreased. These are two points. Next, so we'll discuss about convex sign conventions. We'll discuss So we'll discuss about sign conventions.

[00:52:17]Okay, let's discuss about sign conventions.

[00:52:21]So I'm taking the concave mirror.

[00:52:24]So here you can observe the pole pole focus center curvature.

[00:52:33]All measurements will be taken from the pole in the direction of incident r all are positive. Opposite incident all are negative. Above the principal ais positive below the principal ax is negative. All measurements will be taken in the direction of incident positive.

[00:52:51]Opposite incident is negative. Above the principal ais positive and below the principal axis negative. So like coordinate axis. So here you can take positive x-axis, negative x-axis, positive yaxis, negative yaxis.

[00:53:10]As I coordinate ais how you are taking same you have to take from the concave mirror also. All measurements will be taken in the direction of incident is so positive. Opposite incident is negative.

[00:53:26]So above the principal ais positive and below the principal axis negative. But all measurements must be taken from the pole. Okay. So I hope it is very clear.

[00:53:38]So next one's mirror formula. 1x f = 1x v + 1x u. Magnification equal to height of the image by height of the object minus v by u. So these are the points.

[00:53:51]If you like the content, if you like the channel, do like, share and subscribe to store in the brand. This is part one. So we'll divide into parts because uh it's getting more than 1 hour. Okay. So that part also it will take 1 hour. Okay.

[00:54:08]Maybe 1 and hour 1 hour 1 and 1/2 hour also. Maybe it's nearly 2 and 1/2 hours uh 2 hours to 2 and 1/2 hours it will take. So that why instead of going through a stretch we will divide into parts. Okay. So thank you so much for joining, attending, listening. Do like, share and subscribe to student the brand. This is signing off. Thank you.