Download Light - Effingham County Schools

Light and
Matter
 Prisms
 Colors
 Lenses
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What you see depends on the amount of light in
the room and the color of the objects.
For you to see an object, it must reflect some
light back to your eyes.
Remember reflection occurs when a light wave
strikes an object and bounces off.
Objects can absorb light, reflect light, and
transmit light (allow light to pass through them).
The type of matter in an object determines the
amount of light it absorbs, reflects, and
transmits.
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Opaque material only
absorbs and reflects
light (no light passes
through it).
As a result, you
cannot see the
candle inside.
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Materials that allow
some light to pass
through them are
described as
translucent.
You cannot see
clearly through
translucent
materials.
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Transparent
materials transmit
almost all the light
striking them, so you
can see objects
clearly through
them.
Only a small amount
of light is absorbed
and reflected.
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Refraction causes a
prism to separate a beam
of white light into
different colors.
Remember refraction is
caused by a change in
the speed of a wave as it
passes from one material
to another.
How does the bending of
light create these
colors?
It occurs because the
amount of bending
usually depends on the
wavelength of the light.
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Wavelengths of visible
light range from the
longer red waves to
the shorter violet
waves.
White light, such as
sunlight, is made up of
this whole range of
wavelengths.
The animation shows
what happens when
white light passes
through a prism.
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The triangular prism refracts
the light twice – once when it
enters the prism and again when
it leaves the prism and reenters
the air.
Because the longer wavelengths
of light are refracted less than
the shorter wavelengths are,
red light is bent the least.
As a result of these different
amounts of bending, the
different colors are separated
when they emerge from the
prism.
Which color of light would you
expect to bend the most?
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Does the light leaving
the prism remind you
of a rainbow?
Like prisms, rain
droplets also refract
light.
The refraction of the
different wavelengths
can cause white light
from the Sun to
separate into the
individual colors of
visible light.
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In a rainbow, the
human eye usually
can distinguish only
about seven colors
clearly.
In order of
decreasing
wavelength, these
colors are red,
orange, yellow, green,
blue, indigo, and
violet.
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Why do some apples
appear red, while
others look green or
yellow?
An object’s color
depends on the
wavelengths of light
it reflects.
Remember white
light is a blend of all
colors of visible
light.
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When a red apple is
struck by white light,
it reflects red light
back to your eyes
and absorbs all of
the other colors.
The figure shows
white light striking a
green leaf. Only the
green light is
reflected back to
your eyes.
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Although some objects
appear to be black,
black isn’t a color that
is present in visible
light.
Objects that appear
black absorb all colors
of light and reflect
little or no light back
to your eye.
White objects appear
to be white because
they reflect all colors
of visible light.
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What do your eyes have in common with
cameras, eyeglasses, and microscopes?
Each of these things contains at least one
lens.
A lens is a transparent material with at least
one curved surface that causes light rays to
bend, or refract, as they pass through.
The image that a lens forms depends on the
shape of the lens.
Lenses can be convex or concave.
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Convex lenses are
thicker in the middle
than at the edges.
A convex lens focuses
light at a focal point.
The focal length of
the lens depends on
the shape of the lens.
If the sides are less
curved, light rays are
bent less.
As a result, lenses with
flatter sides have
longer focal lengths.
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The type of image a
convex lens forms
depends on where the
object is relative to the
focal point of the lens.
When the candle is more
than two focal lengths
away from the lens, its
image is real, reduced,
and upside down.
A real image is an image
formed by light rays
that converge to pass
through the place where
the image is located.
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When the candle is between one and two
focal lengths from the lens, its image is
real, enlarged, and upside down.
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When the candle is less than one focal length from the lens,
its image is virtual, enlarged, and upright.
A virtual image is an image formed by diverging light rays that
is perceived by the brain, even though no actual light rays pass
through the place where the image seems to be located.
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A concave lens is thinner
in the middle and thicker
on the edges.
Light rays that pass
through a concave lens
bend outward away from
the optical axis.
The image formed is
always virtual, upright,
and smaller than the
actual object is.
Concave lenses are used
in some types of
eyeglasses and some
telescopes.
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Light enters your eye through a
transparent covering on your eyeball
called the cornea.
The cornea causes light rays to bend so
that they converge.
The light then passes through an opening
called the pupil.
Behind the pupil is a flexible convex lens.
The lens helps focus light rays so that a
sharp image is formed on your retina.
The retina is the inner lining of your eye.
It has cells that convert the light image
into electrical signals, which are then
carried along the optic nerve to your
brain to be interpreted.