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Chapter 15: Refraction
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Refraction refraction: the bending of a wave as it moves from
one medium to another wavefronts f is constant, so as v changes the l must change (must change direction) faster slower Waves bend toward the normal when they slow down!
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Sound Refraction Sound bends toward cooler air (they slow down) so you can hear more clearly across a lake at night.
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Light Refraction Objects appear to be more shallow in water.
soda appears to be at edge of bottle
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Index of Refraction Index of Refraction (n) How fast does light travel
through water?
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Snell’s Law Snell’s Law q1 n1 A ray of light incident in air at 45o
refracts at 32o when it enters another medium. What is the index of the second medium? n2 q2
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Objectives Understand how lenses converge or diverge light rays.
Be able to draw ray diagrams for lenses. Be able to do “lens math.”
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Lenses (from lentils) Lenses can converge or diverge light.
Lenses produce images just like mirrors (but w/ chromatic aberrations) The mirror equations can be used to do lens math. + F F
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Some Ray Diagrams
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Lens Math A 12.4 cm tall candle is placed 16.3 cm from a convex lens with a 25.0 cm focal length. Calculate the image distance, the magnification, and the image height. Describe the image.
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Objectives Know the parts of the eye.
Be able to explain how eyeglass lenses can be used to correct hyperopia and myopia. Understand how a telescope or microscope produces an inverted and enlarged virtual image
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The Eye
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The Eye
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Corrective Lenses Hypermetropia (far-sightedness) is corrected with a convex lens. Myopia (near-sightedness) is corrected with a concave lens.
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Refracting Telescope The eyepiece lens magnifies the real
image produced by the objective lens.
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Objectives Understand the process of total internal reflection and how it relates to refraction. Understand how refraction leads to atmospheric phenomena like mirages and rainbows.
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Total Internal Reflection
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Total Internal Reflection
What is qC for water (1.33) into air (1.00)?
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Atmospheric Refraction: Mirages
object Light refracts away from N in warmer air (speeds up). qC warmer air image
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Dispersion dispersion by a prism: the
index of refraction varies with wavelength (so blue refracts more than red)
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Rainbows Light disperses as it refracts, internally
reflects, and refracts again. The different colors are arranged in a circle between 40o and 42o relative to the anti-solar point or antisun.
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