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Chapter 15

Chapter 15. Reflection and Refraction. 15.1 Reflection of Light. Energized electrons help you see (vibrations emit light) Black absorbs, white emits Law of reflection- angle of reflection equals angle of incidence Normal- perpendicular to reflective surface

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Chapter 15

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  1. Chapter 15 Reflection and Refraction

  2. 15.1 Reflection of Light • Energized electrons help you see (vibrations emit light) • Black absorbs, white emits • Law of reflection- angle of reflection equals angle of incidence • Normal- perpendicular to reflective surface • Incident ray and reflected ray (see picture) • Plane mirror- flat mirror • When mirror is curved, sizes and distances of object and image not equal • Concave vs. Convex • We cannot tell the difference between virtual images (light reaches eye the same)

  3. Diffuse reflection • Only part of light is reflected (4% on glass, 90% on polished metal) • Light on rough surface reflects in many directions- diffuse reflection • If smooth surface, distances between irregularities less than 1/8 wavelength of light, polished • Light on paper diffuse- fibers make incident light reflect off all directions (no glare, like dry road, but wet road is smooth, get glare)

  4. 15.2 Refraction • Light slows when passing through • Light passing from one medium to another- refraction • Light is not perpendicular, bending occurs • Pencil in water • Wave fronts at right angle to ray • Close light source = circular wave fronts • Fish seems nearer to surface than is

  5. 15.3 Illusions • Refraction in Earth’s atmosphere- we see sun after it has passed below us • Light faster in thin air than thick • Sun/moon appears elliptical- near horizon, lower edge bends more than upper edge • Mirage- air hot above surface, cool above that, light travels faster in hot air below, so upward bending as if water (sky)- not mind trick, wavy due to temperature

  6. 15.4 Light Dispersion • Light resonates with electrons of atoms and molecules- opaque • Low frequency light faster in transparent media • Different speeds means different amounts of refraction, so separate or disperse= rainbows • Sun shines on water drops, or prisms that disperse light (on plane, see circular rainbow) • Must look higher to see red • Rainbow seems flat because far away, actually cone if in thick rain with sun behind you • Rainbow moves with you (no gold), but double rainbow if double reflection

  7. 15.5 Lenses • Glass prism diverge to a point • Converging lens (light comes together through thick middle) vs Diverging lens (light spreads, converges on same side as observer) • Greatest deviation at outermost levels, none at middle • Focal point, focal length, center of curvature pictures • See problems

  8. 15.6 Image formation by Lens • No image if overlap • Small opening makes upside-down • Converging lens- magnifying glass (narrow vs. wide angle) • Image appears as if originated at image position- virtual image • Real image- reflected outside focal point of converging lens, upside-down • Diverging makes virtual • Lens defects- aberration- combine lenses • Spherical aberration- light passes through edges of lens, focus at different from center, blurry • Chromatic aberration- different colors have different speeds, image in focus, colors wrong • Pupils contract when too bright • Astigmatism- irregular curvature- more to one side, glasses fix

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