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Current time:0:00Total duration:7:53

Video transcript

let's say I've got some type of a book over here so there is my book I'll write down book let me draw the entire book so this is my entire book just like that and then I have a mirror over here so this is a mirror we're just looking at the mirror from the side I can do a better job of a straight line of that so that is a mirror now what I want to do is pick and I'm really picking an arbitrary point on this book and we know that there's light being shown on there's light being there's light that is coming on this book maybe you know I haven't told us about the light source but we're assuming that the book will reflect the light diffusely like most books do it's it's not a shiny book and so any point on this book and we could pick any arbitrary point on this book it's going to be emitting light in a whole bunch of directions so what I'm just going to do is pick two light rays that are being emitted from this point on the book it'll be more than two but this will help us understand what's going on here so let me pick one light ray that goes like it's obviously not curving like that so it goes like this and hits the mirror incident angle is equal to a reflected angle so it will reflect off at the same angle just like that and let me pick another point that is coming out radially from that same or another ray that is coming out radially from that same point so it'll come out like that it will come out like that it has a larger incident angle so it'll have a larger reflected angle just like that and now let's think about let's think about what an observer someone who has their eyeball right over here so let's say someone has their eyeball right over here so let's think about what this person let me draw their eyebrows so you get the general idea let's think about let's think about what this person right over here will actually see now there I remember you know all of reality is really just a big simulation going on in our brains now this person's eye is going to see these two light rays diverging from some common point if you were to look straight at the book let me just let me just do another example if someone were to just look at any arbitrary object they'll say some time let's say that's orange right over there someone and just ignore all of the stuff on the left if I were to look at an orange no mirror nothing no reflections or anything if I were to look at a certain point on the orange light from that point would be diverging out radially would be diverging out radially and if my eye were right over there if my eye were right over there my brain says okay I have these light rays diverging from a single point it will simulate or it will it will show me that point on an orange in my brain now the same thing is going to happen here even though even though that the light these two rays actually aren't diverging from a point out here your brain will say okay I got two things that are coming out from what looks like a point over here it'll really just extrapolate these lines backwards so it'll take that green ray and I'll say okay it must be coming from a point out there and I'll take that magenta ray and they'll say it must be coming from a point out there whatever you know even here your eye is just seeing these two is just seeing these two light rays it doesn't know what's going on over here just says okay they're just converging from a point and so in this person's reality or in my reality I think that there isn't an orange there likewise I see these two light rays diverging from some common point I will extrapolate to figure out or my brain will try to think about where that point is in three dimensional space it says look these two rays look like they're coming from a point back over here now the reality is there is no back over here that's just that there is nothing we're not assuming there's nothing behind the mirror but to this observer it looks like the light is being emitted behind the observer and so what the person would actually see is something like this the person would actually see would see something like this and this is probably not too far into any of our experiences we've all looked and we've all looked in mirrors and remember this is the left side of this book with this aside sorry this is the right side of the book it's the side that has the curvy part of the B so it'll decide that has a curvy part of the B so it'll look like this so what this observer sees is an image that looks like this it is the what people call the mirror image it is it is flip the left and the right is flipped and you can think about why that is I could just draw another array right here to make it clear if this ray is coming like this now it will reflect and come out back like this to this observer it came it came from that point right over there so he sees a flipped version of the book now the whole reason why I did this is one just to make you feel a little comfortable with these reflecting lines and all of that but one I guess more importantly to get you more comfortable with the idea of a virtual image this right here is a virtual image we're going to compare it with a real image in the next video and so some degree of virtual image is more intuitive because we have so much experience with it when we think about mirrors or reflective surfaces so it's a virtual image and we call it a virtual image because we can't the book really isn't there it's virtually there there is no actual physical space or we don't know if there's any physical space behind the image our brain just uses these diverging lights and creates a model in our inside of our brain or whatever to say okay that book exists there even though the source of the light is over here now I'm just going to draw another diagram and this is more you know you normally won't have the diagrams that have more this type of perspective but just to give you a sense of the same thing and just to get you familiar with some of these diagrams so we're going to do when we study mirrors and lenses is we could imagine that let's say that this is this is the ground let's say that this is a mirror and let's say that this is this is actually could be somebody standing in front of a mirror although usually people will draw an arrow here just say an arbitrary object well let's just say let's say we have an arrow in front of the mirror just so you get used to this notation this is actually a physical arrow this is not a light ray now let's think about what the image of this error let's say this arrow had I so it's actually a person so it's this arrow ad I is what would this arrow see well let's just pick an arbitrary point on this our you could do with any point with this object because every point will be reflecting light and diffusely so I'm going to take one point that's coming straight out of the mirror one light ray that goes straight to the mirror so just parallel to the ground straight to the mirror well it's just going to reflect straight off and then come back it's just going to cut go straight off and then come back to the source of that light maybe that that arrows eye if you view it as a person and let's just do another point another ray coming from that point so another array coming from that point might come out like that incident angle is equal to reflected angle so then it would come back like that now to maybe this whole thing is an eye maybe that'll simplify things maybe this let me make it so let's say this whole thing is you're looking really close at a mirror you're looking really closer to mirror this whole thing is an eye now what would the I see well it's looking this ray looks like it's coming from back over here and then this ray looks like it's coming from back over here this is where they converge so the I would see this point of the eye over there so it will actually see itself it will actually see it will actually see itself and in general these type of diagrams are used to think about what would the real or virtual image be from of an object when once the light from that object goes either is reflected off of a mirror or goes through some type of lens and we'll be doing this a lot more in future videos but anyway hopefully that gets you a little bit familiar with what the things we'll be dealing with