UMass Amherst PHYSICS 132 - Lecture 10 (5 pages)

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Lecture 10



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Lecture 10

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Pages:
5
School:
University of Massachusetts Amherst
Course:
Physics 132 - Intro Physics II
Intro Physics II Documents

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Atreyi Saha Physics 132 Prof Hatch February 10 2016 Lecture 10 Lenses there are two basic types of lenses o converging lenses light rays are being brought together o diverging lenses spreading light rays apart the lens is made of some transparent material and usually both sides of the lens are spherical o there are two types of surfaces convex or concave When light comes from a long distance the light rays are effectively parallel A converging lens is a convex lens is equivalent to two prisms o convex surfaces converge light to a point known as the focal point o light will converge at the focal point if light rays coming in are parallel o because the sun is so far away all the light rays from the sun are parallel o convex lenses take the parallel rays and focus the light o light rays that are coming in from much closer are not going to be parallel and thus the light will not be focused at a focal point A diverging lens is a concave lens and you can also liken it s behavior to two prisms o The lens spreads the light out as if the light came from the focal point o Once again this applies to parallel light Signs of lenses o Converging lens positive o Diverging lens negative This is because the focal point here is virtual with lenses if something is real it is positive if something is virtual it is negative like in this case Real vs Virtual Images o When you look at a flat mirror the image is behind the mirror No light actually there Light APPEARS to be there Where light appears to be and not there that is what we call virtual So your image in a flat mirror is virtual o A real image forms where real light ends up Ray diagrams for lenses we want to sketch where things are o Image is formed where two light rays cross o Parallel ray is a ray that is parallel to the lens optical axis middle line through the lens on incidence and after refraction either a passes through the focal point on the image side of a converging lens or b appears to diverge from the focal point on the



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