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# Lenses

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### Lenses

1. 1. Lenses
2. 2. Lens: <ul><li>A curved , transparent material that is regularly shaped </li></ul><ul><li>Refracts light in a predictable and useful way </li></ul>
3. 3. Lenses <ul><li>Made of transparent glass or hard plastic </li></ul><ul><li>Can be shaped and polished to control how the light rays converge or diverge </li></ul><ul><li>Used to magnify images or project images onto a screen </li></ul>
4. 4. Vocab: <ul><li>Axis of Symmetry - an imaginary vertical line drawn through the optical center of a lens </li></ul>
5. 5. Vocab: <ul><li>Principal Foci </li></ul><ul><ul><li>F - where the light rays (appear to) converge </li></ul></ul><ul><ul><li>F’ - same distance as F, but on the opposite side of the lens </li></ul></ul><ul><li>Focal Length ( f ) - distance from the principal focus to the axis of symmetry </li></ul>
6. 7. Concave Lenses <ul><li>Thinner at the center , thicker at the edges </li></ul><ul><li>Diverging </li></ul>
7. 9. Concave Lenses <ul><li>The image formed is always virtual , upright and smaller </li></ul>
8. 10. Concave Lens Ray Diagrams Ray 1 - travels from the tip of the object parallel to the principal axis . When it emerges from the lens, it appears to come from the principal focus ( F )
9. 11. Concave Lens Ray Diagrams Ray 2 - travels from the tip of the object through the optical centre of the lens and is not refracted .
10. 12. Concave Lens Ray Diagrams The image occurs where these rays appear to intersect .
11. 13. Convex Lenses <ul><li>Thicker at the center , thinner at the edges </li></ul><ul><li>Converging </li></ul>
12. 15. Convex Lenses
13. 16. Convex Lens Ray Diagrams Ray 1 - travels from the tip of the object parallel to the principal axis . When it emerges from the lens, it travels towards the principal focus (F)
14. 17. Convex Lens Ray Diagrams Ray 2 - travels from the tip of the object through the optical centre of the lens and is not refracted .
15. 18. Convex Lens Ray Diagrams The image occurs where these rays appear to intersect .
16. 19. Convex Lens Ray Diagrams <ul><li>4 Cases: </li></ul><ul><li>Object is greater than 2 focal lengths from the lens (d o >2 f ) </li></ul><ul><li>Object is between 1 and 2 focal lengths from the lens (f< d o <2 f ) </li></ul><ul><li>Object is at the focal point (d o = f ) </li></ul><ul><li>Object is less than 1 focal length away from the lens (0<d o < f ) </li></ul>
17. 20. Case 1: Real Reduced Inverted Attitude Size Type
18. 21. Case 2: Real Enlarged Inverted Attitude Size Type
19. 22. Case 3: No Image Formed! Attitude Size Type
20. 23. Case 4: Virtual Enlarged Upright Attitude Size Type