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Lenses Focal Point Focal Length Animation of Light in a Lens.

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Presentation on theme: "Lenses Focal Point Focal Length Animation of Light in a Lens."— Presentation transcript:

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2 Lenses

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4 Focal Point Focal Length

5 Animation of Light in a Lens

6 Ray Diagrams for Converging Lenses 1. Parallel incoming light is refracted through the focal point

7 2. Light coming in through the focal point is refracted out parallel

8 3. Rays passing through the center are refracted out in the same direction. 4. An image is formed where the rays cross.

9 A parallel beam of light is sent through an aquarium. If a convex glass lens is held in the water, it focuses the beam… 1.closer to the lens than… 2.at the same position as… 3.farther from the lens than… …before.

10 A parallel beam of light is sent through an aquarium. If a convex glass lens is held in the water, it focuses the beam… 1.closer to the lens than… 2.at the same position as… 3.farther from the lens than… …before. The index of refraction (n) between water and glass is less than it is between air and glass. Therefore the light in the water bends less and if focused farther away.

11 A real image is one where the light rays actually come from the image location. Real Image

12 Virtual Image A virtual image is one where the light rays do not actually come from the image location, but rather only seem to.

13 Lens Equations: Distances & Focal Points: Focal Length for a converging lens is positive (+). There is something called a diverging lens which has a negative focal length, but we have not (& will not) talk about that type of lens.

14 Sign Conventions QuantitysymbolFrontBack Object Location p+- Image Location q-+ Focal Length f+- Converging Diverging (not doing diverging lenses in this class)

15 QuantitysymbolFrontBack Object Locationp+- Image Locationq-+ Focal Lengthf+- Real Image Front of lens Back of lens Object is in front of the lens so p = + Image is behind the lens so q = +

16 Front of lens Back of lens Object is in front of the lens so p = + Image is on front of the lens so q = - Virtual Image QuantitysymbolFrontBack Object Locationp+- Image Locationq-+ Focal Lengthf+-

17 Lens Equations: Magnification Note the negative sign

18 QuantitysymbolUpright Image Inverted Image Image Height h’+ Magnification M+ If M is < 1 the image is smaller than the object If M is > 1 the image is larger than the object Signs for magnification

19 Real Image QuantitysymbolUpright Image Inverted Image Image Height h’+ Magnification M+ Image is inverted (upside down) therefore h’ = -

20 The lens projects an image of the candle on a wall. How will the image differ if the top half of the lens is covered with a red filter and the bottom half with a green filter? Lens

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