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Journal 2/5/14

Journal 2/5/14. We've done enough ray diagrams you may be able to figure the next one out. See if you can do a ray diagram for a concave lens with the object farther than the focus. Objective Tonight’s Homework. To learn ray diagrams for concave lenses. pp 388: 9, 10, 11. Concave Lenses.

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Journal 2/5/14

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  1. Journal 2/5/14 We've done enough ray diagrams you may be able to figure the next one out. See if you can do a ray diagram for a concave lens with the object farther than the focus. Objective Tonight’s Homework To learn ray diagrams for concave lenses pp 388: 9, 10, 11

  2. Concave Lenses All concave lenses: These are different. Only one ray will go through a focal point. Ray 1: Draw diagonally through the center of the lens. It just goes straight.

  3. Concave Lenses All concave lenses: These are different. Only one ray will go through a focal point. Ray 1: Draw diagonally through the center of the lens. It just goes straight. Ray 2: Draw horizontal to the plane, then bending upward. To get the angle, trace back from the lens to the near focal point.

  4. Concave Lenses All concave lenses: These are different. Only one ray will go through a focal point. Ray 1: Draw diagonally through the center of the lens. It just goes straight. Ray 2: Draw horizontal to the plane, then bending upward. To get the angle, trace back from the lens to the near focal point. Our image is virtual and upright.

  5. Concave Lenses All concave lenses: Note that this ends up the same even if we move the object closer than the focal point. It is not possible to create a real image from a concave lens!

  6. Concave Lenses Let’s see an example of how these lenses work for people that need glasses (or contacts.) Normally, the eye takes incoming parallel light and bends it with a convex lens (the cornea) to the back of the eye (the retina). This focuses an image. However, a nearsightedperson’s cornea can’t bendenough. This means far things don’t focus.

  7. Concave Lenses Glasses introduce a concave lens. This lens spreads the light out just a bit so that when it hits the eye it has more distance to go before focusing. This moves the focal point back to the retina, allowing you to see in focus. If you’re farsighted, we get the same process, but with a convex lens instead of concave.

  8. Practice pp 701: 16, 17, 18

  9. Exit Question #16 What will happen in the imageshown at right? a) It will still focus on the left, but closer than normal b) It will still focus on the left, but farther away c) It will never focus d) It will focus far to the right e) It will focus close to the right f) None of the above

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