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75475_lecture02A - March 23, 2010 Physics 214: Images Today...

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Unformatted text preview: March 23, 2010 Physics 214: Images Today Geometrical Optics : tracing the geometry of light rays to understand how images are formed and how they can be manipulated- Mirrors- Lenses- Telescopes, microscopes, cameras, etc. Quite complex Feld, we will only scratch the surface of it 3 March 23, 2010 Physics 214: Images Images When we see an object, our eyes are detecting light emerging or refecting From the object Our brains know that light travels in straight lines, so we determine the direction oF the object by instinctively extrapolating backwards along the direction From which the light arrived Binocular vision lets us compare two slightly diFFerent directions to determine distance 4 eye light ray March 23, 2010 Physics 214: Images Images Unfortunately, our brains are wrong- Light does NOT always travel in straight lines ReFection and refraction mean that the location determined by our brain extrapolating back may not be the real location of the object The false object our brain perceives to exist is called the image of the object We can predict what we will perceive by tracing the lights actual path from the object to our eye, and then calculating what our brain will do with the light we see 5 March 23, 2010 Physics 214: Images Images Images come in two general types: Real images- Are (or could be) formed on a surface, such as a projection screen, a piece of Flm, or the retina of your eye Virtual images- Seem to exist in their perceived location only because of the way the light is manipulated and the way it is interpreted by an observer- The light rays dont actually come from or pass through the image 6 March 23, 2010 Physics 214: Images Virtual Images: Plane Mirror 7 eye Plane mirrors (like the one in your bathroom) create virtual images The eye sees the image of object O behind the mirror at point I- The location of this point is independent of the eyes position Light appears to be emerging from inside the wall obviously this is not really happening March 23, 2010 Physics 214: Images Plane Mirrors The image is perceived to lie a distance i behind the mirror What is the relationship between i and p ?- Pick out two of the rays in the diagram- The two right triangles have one equal side and all angles equal, so they are congruent: length I b = length O b Convention: i = p (distances to virtual images, like i , are negative) 8 Note: used angle of incidence = angle of reFection March 23, 2010 Physics 214: Images Images Whats the advantage of analyzing these phenomena in terms of images? Observers at (almost) any position will agree on the apparent location of the object they all see the same image- Once we know where the image is, we can forget about the real object entirely (for most purposes)- Its as if the image were the only real object- (Obviously, this is not true in absolutely all cases for example, doesnt hold for an observer on the wrong side of the mirror) 9 March 23, 2010...
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This note was uploaded on 05/23/2011 for the course MATH 130 taught by Professor Page during the Spring '11 term at Imperial College.

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75475_lecture02A - March 23, 2010 Physics 214: Images Today...

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