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Refraction and Lenses

Refraction and Lenses. refraction : the bending of light as it travels at an angle from one transparent medium into another. less. When light goes from a… dense medium. more. more. to a… dense medium,. less. toward. it bends… the normal. away from.

judah-mclaughlin
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Refraction and Lenses

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  1. Refraction and Lenses

  2. refraction: the bending of light as it travels at an angle from one transparent medium into another less When light goes from a… dense medium more more to a… dense medium, less toward it bends… the normal. away from It has been found that light obeys the principle of least time.

  3. angle of incidence, Qi normal incident ray refracted ray Qi for 2nd boundary angle of refraction, Qr Qr for 2nd boundary AIR (less dense) GLASS (more dense) AIR (less dense)

  4. “ZAP!” AIR (less dense) GLASS (more dense) “LASER…” AIR (less dense) “Costing one MILLION dollars…”

  5. Index of Refraction n = index of refraction; c = 3.00 x 108 m/s; v = velocity of light in mat’l (m/s) In general... n > 1.000. Snell’s Law incident medium (ni) Qi refracting medium (nr) Qr

  6. Light in air is incident on diamond (n = 2.419) at 43.0o. Find the angle of refraction. 43.0o n = 1.000 n = 2.419 Qr = 16.4o

  7. Light in water is incident on cubic zirconia at 31.5o. Angle of refraction is 18.5o. Water’s index of refraction is 1.333. Find velocity of light in cubic zirconia. 31.5o n = 1.333 nr = nc.z. = ? 18.5o = 1.37 x 108 m/s

  8. image actual path of light object • Examples of Refraction atmospheric refraction We continue to see the Sun after it has set. Earth …n increases in lower atmosphere, so light bends more and more

  9. object actual path of light image • Examples of Refraction (cont.) mirages …not an optical illusion; can be photographed …“water” on road is an image of sky

  10. Lenses Types of Lenses converging lensesdiverging lenses double convex double concave plano-convex plano-concave concavo-convex convexo-concave

  11. F F F F Lens Ray Diagrams First… 1. Draw a centerline vertically through lens. 2. Draw two F’s on the P.A. Rules: through F parallel to P.A. “NOT!”

  12. f = focal length CONVERGING,+ R = radius of curvature DIVERGING,– real image: rays actually intersect; can project it on a screen virtual image: rays appear to intersect, but don’t; cannot project it on a screen p = object dist. always on LEFT; always + q = image dist. RIGHT,+,REAL; LEFT,–,VIRTUAL h = object height always UPRIGHT; always + h’ = image height UPRIGHT,+; INVERTED,–

  13. Lens Equations Sign Conventions Thin Lens Equation and Magnification

  14. Diverging lens? “SUV.” Diverging lens has focal length 10.0 cm. A wiener-dog puppy 15.0 cm tall is 22.0 cm from lens. Describe image. (f = –10.0 cm; h = 15.0 cm; p = 22.0 cm) = – 6.88 cm = 0.313  h’ = 0.313(15) = 4.70 cm SMALLER; UPRIGHT; VIRTUAL; on the left

  15. –0.38 cm Converging lens has focal length 7.7 cm. A 0.38 cm-tall real image of a thimble is formed 9.1 cm from lens. How far from lens is thimble? How tall is thimble? (f = +7.7 cm; q = +9.1 cm) h’ = –0.38 cm; = 50. cm = –0.18 h = 2.1 cm

  16. retina cornea incoming rays from distant objects incoming rays from nearby objects • Correcting Vision with Lenses farsightednearsighted What is in focus?

  17. diverging lens converging lens What is blurred? nearby objects distant objects How do we correct the condition?

  18. Total Internal Reflection Light traveling through water (n = 1.333) is incident on the water/air boundary at 48.606626o. Find angle of refraction. = 90.0o

  19. refracted rays boundary Qc • The Critical Angle, Qc the Qi for which Qr = 90o normal (LESS dense medium) (MORE dense medium) reflected ray

  20. -- light is incident from MORE dense medium to a LESS dense medium at Qi > Qc light exiting light entering total internal reflection -- no light escapes from MORE dense medium e.g., T.I.R. in fiber optic cables

  21. crown glass flint glass Equation for the Critical Angle Find critical angle for light traveling from flint glass (n = 1.900) to crown glass (n = 1.522). = 53.23o

  22. n differs for different ls Dispersion when polychromatic light is separated into its component ls occurs because different ls interact differently w/matter -- -- -- By convention, the accepted index of refraction for a material is for l = 589 nm.

  23. WHITE The various ls traveling through a lens focus at slightly different points; resulting blurring = chromaticaberration R F F 589 nm V combining converging and diverging lenses made from different types of glass -- reduced by...

  24. h h

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