Transcript Chapter 14 Refraction ppt

Refraction & Lenses
Refraction
• The change in direction of a wave as is
crosses the boundary between two media in
which the wave travels at different speeds.
Index of Refraction
speed of light in vacuum
n
speed of light in material
Snell’s Law
n1 sin 1  n2 sin 2
Index of Refraction
Material
Vacuum
Air
Ice
Water
Ethyl Alcohol
Plexiglas
Crown Glass
Light Flint Glass
Dense Flint Glass
Zircon
Diamond
Rutile
Gallium phosphide
Index of Refraction
1.0000
1.0003
1.3100
1.3330
1.3600
1.5100
1.5200
1.5800
1.6600
1.9230
2.4170
2.9070
3.5000
Lenses
Converging Lens
Rules For Converging Lenses
1) Any incident ray traveling parallel to the
principal axis of a converging lens will refract
through the lens and travel through the focal
point on the opposite side of the lens.
2) Any incident ray traveling through the focal
point on the way to the lens will refract through
the lens and travel parallel to the principal axis.
3) An incident ray which passes through the center
of the lens will in effect continue in the same
direction that it had when it entered the lens.
Image Formation by Converging Lens
Diverging Lens
Rules For Diverging Lenses
1) Any incident ray traveling parallel to the
principal axis of a diverging lens will refract
through the lens and travel in line with the focal
point (i.e., in a direction such that its extension
will pass through the focal point).
2) Any incident ray traveling towards the focal
point on the way to the lens will refract through
the lens and travel parallel to the principal axis.
3) An incident ray which passes through the center
of the lens will in effect continue in the same
direction that it had when it entered the lens.
Diverging Lens Image Formation
Always Virtual, Smaller, and Right-Side Up
Optical phenomena
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Dispersion
Total Internal Reflection (TIR)
Critical angle and periscopes
Fiber optics
Chromatic abberation
Dispersion
• The separation of light into colors arranged
according to their frequency, by interaction
with a prism or diffraction grating.
Rainbows
• Perhaps the most spectacular and best known atmospheric
optical phenomenon is the rainbow.
• Sunlight and water droplets are necessary for the formation
of a rainbow.
• Furthermore, the observer must be between the Sun and
rain.
• When a rainbow forms, the water droplets act as prisms
and refraction disperses the sunlight into the spectrum of
colors, a process called dispersion.
• The curved shape of the rainbow results because the
rainbow rays always travel toward the observer at an angle
between 40 and 42° from the path of the sunlight.
Rainbows
• White light separates into different colors
(wavelengths) on entering the raindrop because
red light is refracted by a lesser angle than blue
light. On leaving the raindrop, the red rays have
turned through a smaller angle than the blue rays,
producing a rainbow.
Why is a Rainbow Curved?
Total internal
reflection (TIR)
Fiber optics
Chromatic aberration
Occurs for converging lenses and arises because the index of refraction of
the lens material varies with wavelength.
--colors pass through lens and refract at different angles
--this is related to dispersion
--a blurred image like below is produced
Aurora borealis
• Optical phenomena in
the atmosphere is
varied and can be awe
inspiring.
• Can range from auroras
to halos, sun pillars to
green flashes.
• Aurora borealis is caused
by the collision of
energetic charged
particles with atoms in
the high altitude
atmosphere
Auroras - interaction of the Sun’s particles (solar
wind) and the magnetosphere of Earth.
Green Flash
(not the comic-book character)
• Seen on upper rim of rising
or setting sun (more
common). There is so much
atmosphere to penetrate
when sun is on horizon,
sunlight is refracted. Purple,
blue bend the most, red the
least. Blue light should
appear at top of sun, but blue
light is scattered selectively,
so green light is seen.