Light and Living Things

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Light is a form of energy—like heat and
sound.
Light and Living Things
Light can be reflected, refracted,
transmitted, and absorbed by matter.
The angle of reflection of a light beam
is equal to the angle of incidence.
• Light given off from
objects, like a light bulb
or the Sun, travels in
straight
g lines.
• Each light ray
represents a thin beam
of light and is drawn
with an arrow head
that shows the
direction of travel.
What happens when light hits a
different material?
• Light travels in straight lines through a
material (like air) until it hits a different
material.
• Then,
Then it can be absorbed,
absorbed reflected,
reflected or
transmitted (which means “passed
through”).
• Usually, all three things happen.
You can see the glass and the reflection in it
because light is reflected off the glass.
You can see the trees outside because light
is transmitted through the glass.
The glass is warm to the touch because some
light is absorbed by the glass.
1
Absorption
• When light is absorbed, its energy is
transferred to the absorbing material.
• Black objects absorb almost all of the light
that falls on them. That is why a black road
surface
f
gets h
hot on a sunny d
day. Li
Light
h
energy from the Sun is absorbed by the
road.
Why then, since most objects do not
emit their own light, can we see them?
• Objects that do not emit their own light
must reflect light in order to be seen.
• Reflection occurs when light bounces off of
a surface.
Reflection involves two rays - an
incoming and an outgoing ray.
Normal Line is the line
between the beams
perpendicular to the mirror.
angle of the
incidence ray
• The incident ray is the light ray that strikes
the surface of the mirror.
• The reflected ray is the light ray that
bounces off the surface of the mirror.
Law of Reflection
angle of the
incidence ray
angle of the
reflected ray
Flat, mirrored surface
Regular reflection
angle of the
reflected ray
Flat, mirrored surface
• The angle of reflection of a light beam is
equal to the angle of incidence.
• When you look in a mirror,
you can see your image
because when parallel light
rays hit the mirror at the
same angle, they are all
reflected at the same angle.
• This is called regular
reflection.
2
Scattered reflection
• You can’t see your image
when you look at a white
piece of paper because even
though it seems smooth, its
surface has tiny bumps on it.
• When parallel light rays hit a
bumpy surface, the bumps
reflect the light rays at
different angles.
Light rays reflected at different angles
cause scattered reflection.
• Many surfaces, for example, polished wood,
are in between rough and smooth and
create both types of reflection.
3
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