Reflection, Refraction,
and Absorption
Light travels in a straight line. What happens when
it hits an object???
It can bounce back (reflect), bend (refract), or be
absorbed (absorb) by the object.
Reflection
• Reflection occurs when an
object or wave bounces back
off a surface through which it
can not pass.
• What sort of objects reflect
light?
•
•
•
•
Mirrors
Shiny surfaces
Some metal
Surface of water
Law of reflection
 The law of reflection states
the angle of incidence equals
the angle of reflection.
 The angle of incidence (angle
of the incoming wave) is the
same as the angle of
reflection (angle of the
reflected wave).
 Notice on the diagram to the left how on
a smooth surface, the light bounces back
at the same angle it hits the surface.
Plane Mirrors
 Plane mirrors- A flat sheet
of glass with a silver coating
on one side. When light
strikes the coating the
image and the light is
reflected back.
 The image produced is a
virtual image, which is
upright and reversed
Concave Mirrors
 Concave Mirror: A mirror with a surface that curves
inward. (Think “cave”)
 Example: makeup mirrors (they enlarge the image), inside
of a spoon.
 This gives these mirrors the ability to create an
image when their curvature bounces light to a
specific area in front of them. This area is called
the focal point.
 From far away, objects will seem upside down, but
as you get closer and pass the focal point, the
image flips and magnifies.
Concave Mirrors
 Reflecting telescopes
use a concave mirror
instead of an objective
lens to gather light
from a distant object.
 Used by astronomers
 Invented in the 1600s
Convex Mirror
• Convex Mirror: A mirror with a
surface which curves outward.
• This gives a wide field of view
and is used in security mirrors in
stores as well as side mirrors on
cars.
• The image in a convex mirror is
always upright and is smaller
than the object.
Convex Mirror
Refraction
• When light waves bend when
passing through one substance to
another, this is refraction.
• When light rays enter a medium at
an angle, the change in speed
causes the light rays to bend, or
change direction.
• What sort of objects refract
light?
•
•
•
•
•
Prisms
Cut diamonds
Water
Soap bubbles
Microscope lenses
Absorption
• When light is absorbed by an object this is usually when
light transfers its energy into another form (like heat).
• Have you ever worn a black shirt on a sunny day? What
happens? Do you feel the light energy turn into heat?
What sort of objects absorb
light?
Technically most items do
absorb some light. In fact, the
color does matter! When we
see an object that is green that
is because the object is
absorbing all of the colors
EXCEPT for green. Green is
bounced back to our eye and
we see a green object.
How does a rainbow form?
First, what
things are
needed for a
rainbow to
form?
Refraction =
Waves changing direction as they travel
from one material to another.
Mini-Lab: Refraction in Water
Viewing from the side, draw picture of pen/pencil
in empty beaker. Then add water and draw again.
Why does the pencil bend in the water?
Refraction! Light waves travel at DIFFERENT
SPEEDS through air and water.
So waves travel at different speeds through air
and water
.......and rainbows need light and rain...so....
Rainbows form when light is refracted off
raindrops. If the sun is at the correct angle,
different drops will refract different colors.