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Video transcript

we've talked a lot about convex lenses so I thought I would do a quick video on concave in lenses although there aren't as many different combinations of what a concave lens can do so just remember concave has the word cave in it so I always imagine that it's kind of caving in Words caving in where it's a little bit of an exaggerated drawing I think you get the general idea this is a concave lens right over here and let me draw its principal axis so this is its principal axis it shouldn't curve at the beginning let me just redraw it so that's its principal axis and let me draw the two focal points let me draw one over here on the left side and then let equal distance focal point on the right side and I'm assuming that the two surfaces are they're both concave and they're symmetric over here that's just assumption I'm making now let's think about what's going to happen if I put an object if I put an object someplace on someplace on the left side of this concave lens so I'll you could put it let me just stick it anywhere so let me stick it right over there so if I do and like always we'll do our two rays but with the concave lens what I'm going to do I'm going to raise I'm gonna do one that's parallel to the principal axis and then I'm going to do one that does not get diffracted so it goes right through the center of the lens and let's think of what would happen so if we go parallel if we go parallel to the principal axis this will get diffracted away since it's coming in parallel it'll get diffracted and we'll get diffracted outwards so that it looks like it's coming from this focus so it'll get diffracted in a way so it looks like it's coming from that focus so it's getting diverged outward I guess we could say and let me draw another let me draw another point or another ray I should say I'll do that in yellow and this one's just going to go straight through the center of the lens and not get diffracted so it's just going to go straight through the center of the lens and not get diffracted so what will the image be here well clearly these two rays don't converge so we won't have a real image but they do both look like they're diverging from someplace and they look like they're diverging they look like they're diverging from right over there so whatever so look to an observer out here if their eyeball is right over there it looked to an observer I could draw their nose just make it clear what the person who where where the eye is if they look at from this side they're going to see a virtual image of the object right right over here just like that so what you're actually going to see is a virtual image of the object that is not inverted and it's going to be smaller it's going to look like it's closer to the lens than it really is anyway that's that's all there really is to know I mean there's obviously there's a lot you can know about anything but but that's the general gist of a concave lens