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Refraction, Lenses, & Sight
Refraction
• The change in direction of a wave as it
crosses the boundary between two media in
which the wave travels at different speeds.
Dispersion
• The separation of light into colors arranged
according to their frequency, by interaction
with a prism or diffraction grating.
The Human Eye
The Human Eye
How do you see!!!
• You see light through a series of steps that
involve both the eye & the brain.
• Light enters the eye through the pupil. (black
circle in center of your eye)
• It is black because all light is _______ by black.
• The colored area around the pupil (the iris),
controls the amount of light that enters the
pupil.
• The light that enters the eye is refracted and
focused on the curved rear surface of the eye.
• The image that is formed is upside down and
smaller than the object.
• Most of the refraction takes place in the cornea,
the protective outer covering of the eye.
• The lens of the eye makes adjustments for
focusing on objects at different distances.
• The muscles (sclera) relax the lens to see far off
and contract to see up close. (Thin & Thick)
Check out the brain
• The image that falls on the light sensitive
retina is transferred by the nervous system
and interpreted by the brain.
• Some of the nerve cells in the retina are
called rods. Rods are sensitive to light &
dark
• Other nerve cells called cones allow us to
see color.
Normal Eye Focus
Astigmatism
• Cornea is oval shaped instead of spherical.
This causes light to focus on two or more
spots.
Near-Sighted (Myopia)
Far-Sighted (Hypermetropia)
Corrections:
• Farsighted people can see objects at a
distance, but not up close. To correct this
problem they must wear a convex lens.
• Nearsighted people can see objects close up,
but can not see at a distance. To correct this
problem they must wear a concave lens.