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Refraction Phenomena

Refraction Phenomena. Apparent Depth & Volume. Refraction can change the perception of depth and volume because the apparent path of light does not equal the actual path of light. Underwater Vision. Atmospheric Effects. Longer Sunsets. Twinkling Stars. other atmospheric effects.

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Refraction Phenomena

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  1. Refraction Phenomena

  2. Apparent Depth & Volume Refraction can change the perception of depth and volume because the apparent path of light does not equal the actual path of light.

  3. Underwater Vision

  4. Atmospheric Effects Longer Sunsets Twinkling Stars other atmospheric effects Green Flash

  5. Mirages A mirage (or looming) occurs when the air temperature near the Earth’s surface differs greatly over thin layers.

  6. Mirages Sound “Mirage” Light Mirage

  7. Dispersion Dispersion is the separation of white light into colors, called a spectrum violet red Newton theorized that corpuscles of light refracted according to color. Robert Hooke (and others) theorized that waves of light refracted according to color

  8. Chromatic Aberration The consequence of dispersion in lenses is a color distortion called chromatic aberration click for applet uncorrected lens apochromatic lens

  9. Rainbows Rainbows are caused by dispersion of white light into a spectrum of colors within drops of rain click for applet RAINBOW DIAGRAM DOUBLE RAINBOW DIAGRAM

  10. Dispersion Phenomena SUN HALO SUN DOGS CIRCUMHORIZONTAL ARC MOON HALO

  11. Total Internal Reflection click for applet click for applet

  12. Critical Angle Total Internal Reflection occurs if light tries to refract into a less optically dense medium than it starts in, and only if the incident angle exceeds the critical angle. For example, light can totally internally reflect within water as it attempts to refract out into air if θi > θc. It can never do T.I.R. going from air to water. To find the critical angle use Snell’s Law:

  13. TIR Applications -Fiber Optics ENDOSCOPES USING TIR

  14. Other TIR Applications DUAL PRISM BINOCULARS “FRUSTRADED” TIR PERISCOPE

  15. Diamonds Diamonds produce rainbows by dispersion and total internal reflections (two or more).

  16. Human Vision Cornea - protects the eye; does 70-80% of focusing, index n = 1.38 Pupil - eye’s (black) opening Iris - eye’s (colored) aperture which controls light entering eye Lens - does 20-30% of focusing; index n = 1.44; shape controlled by muscle Aqueous humor- fluid behind cornea Retina - detects light intensity with rods (for low level black and white vision) and detects light frequency with cones (for color) Fovea - region where rods/cones are most concentrated; images are typically focused at the fovea, about 1.7 cm behind cornea Optic nerve- network of nerve cells that connects light signals from the retina to the brain, causes a subtle “blind spot” Vitreous humor- fluid that fills cavity between the lens and retina

  17. Accommodation The eye can’t focus by changing the distance between cornea/lens and the retina. It must change the focal length of the lens, called accommodation. For nearby objects the lens is squeezed into a more curved shape; for distant objects the lens is relaxed into a less curved shape. Nearsightedness (myopia) is the inability of the eye to focus on distant objects, caused by a bulging cornea or an elongated eyeball. A diverging (negative) lens is used to correct nearsightedness. Farsightedness (hyperopia) is the inability of the eye to focus on nearby objects, caused by weakening of ciliary muscles or decreased flexibility of the lens (presbyopia) . A converging (positive) lens is used to correct farsightedness. click for applet

  18. Accommodation ACCOMMODATION NEARSIGHTED FARSIGHTED

  19. Common Vision Problems Astigmatismis caused by a cornea (or lens) with irregular curvature, shaped more like a football than a basketball. Corrective lenses or refractive surgery will restore vision. Cataracts are clouding of the lens; common for elderly, but also congenital, environmental, or trauma related. Lens replacement (surgery) is effective. Color blindness is from a lack or malfunction of one or more types of cones, commonly those tuned to red light. Many other types exist. Corrective lenses can be effective.

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