7/20/2009
Name some transparent materials.
Refraction
Light
Li
h travels
l iin straight
i h li
lines if the
h
medium it travels through does not
change.
When a light ray traveling through air
enters glass it slows down.
• This slowing down of light when it goes
from air to water or from air to glass
causes the light
g ray
y to bend or refract.
This bending effect takes place whenever
light slows as it moves from one material into
another.
• Light traveling from air and going into water
would be another example.
• Transparent materials like air, glass, and
water allow light to be transmitted.
• However, almost every time light passes
from one type
yp of matter into another, it will
change speed.
• For example, light travels slightly faster in
air than in water.
Refraction is the bending of light as it
crosses a boundary between two
different transparent materials.
If you’ve ever tried to grab a fish
underwater you know how hard it can
be.
• Why? Because the fish’s apparent position
is changed by light refraction at the airwater boundary.
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7/20/2009
To measure how much a light ray
refracts, a reference line is needed.
• This line is called
a normal line.
• A normal line is
an imagined line
perpendicular to
the surface is at
the point of
refraction.
The opposite effect happens when light
speeds up as it moves from one material
into another.
• For example, when
light goes from glass
or water to air, it
speeds up.
Therefore, when a light ray traveling
through air enters water or glass it slows
down, refracts, and bends toward the
normal line.
Refraction changes how objects
look.
• A glass rod in water
is a good example of
refraction.
• The glass rod appears
to break where it
crosses the surface of
the water, but this is
just an illusion.
• The illusion is caused
by refracted light
rays.
The light rays from the glass rod are
refracted (or bent) when they cross from
water, into glass, and back into air
before reaching your eyes.
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