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Focus

Focus. An object moved far to the left approaches a parallel ray source. s o = ∞ . The image approaches the focal point f of the lens. Distant Source. R 2. R 1. s o. f. object. image. A biconvex lens is a positive lens. Both terms are positive R 1 > 0 and R 2 <0

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Focus

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  1. Focus

  2. An object moved far to the left approaches a parallel ray source. so = ∞. The image approaches the focal point f of the lens. Distant Source R2 R1 so f object image

  3. A biconvex lens is a positive lens. Both terms are positive R1 > 0 and R2 <0 Converging lens Focal length is positive If the radii are small, the focal length is roughly equal to the smaller radius. Positive Lens

  4. A biconcave lens is a negative lens. Both terms are negative R1 < 0 and R2 > 0 Diverging lens Focal length is negative Negative Lens R1 R2 so f object image

  5. Parallel rays may enter the lens at a small angle. Focal points on a line This defines the focal plane. Focal Plane R2 R1 so f object image

  6. Underwater • A glass lens is held underwater to view an object at the bottom of the tank. The focal length will be • A. longer. • B. about the same. • C. shorter.

  7. Real Image • Rays through a converging lens can meet at a focal plane and form a real image. • Object between f and 2f from the lens forms past 2f on far side • Screen elsewhere has blurred image Thin lens equation

  8. Virtual Image • Rays through a diverging lens create no real image. • Virtual image from apparent origin • Focal length and image point are negative next

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