Interactions of Light with Matter
Chapter 3 Section 2
How does light travel?
• In a straight line
unless it hits object or
is absorbed
What is reflection?
• Light bouncing off an
object
• Changes direction of
light
• Like a ball bouncing
off ground
What is “Law of Reflection”?
• Angle made by light hitting surface =
angle of light reflected
What are the types of
Reflection”?
• Regular reflection: light reflects off mirror at
same angle; surface smooth/ shiny – mirror
What are the types of
Reflection?
• Diffuse reflection: light
reflects in many
directions; surface
rough/bumpy – wall;
can’t see reflection
What are the types of
Reflection?
• Regular
(Spectacular)
• Diffuse
What are the light sources?
• Luminous - object
produces visible light
• Illuminated – object
needs a separate light
source to be seen
• Importance? Sight needs
light; to be seen must
either be luminous or be
illuminated
Interactions of Light with Matter
Chapter 3 Section 2 Part II
What is absorption of light?
• Transfer of energy to
particles of matter
• Explains why light
dims as it moves from
light source: more
particles absorb the
energy, making it
dimmer
What is scattering of light?
• Light moving in all
directions after
colliding with particles
• Fog is good example
• Allows you to see
outside beam, but it
dims
• Explains why sky is
blue: shorter wavelength is
scattered more than other colors,
so you see more of it
How does light interact with
matter?
• Reflected – bounces off
• Transmitted – passes
through matter; example
through a window
• Absorbed – transfer light
energy to matter; makes
object feel warmer
• (next section) Refracted –
wave is bent
How does transparent, translucent,
or opaque matter matter? 
• Transparent: easily
transmits visible light (air,
glass, H2O)
• Translucent: transmits light
but also scatters it (wax
paper)
• Opaque: doesn’t transmit
light (metal, wood, textbook)
How is an object’s color
determined?
• Wavelength determines
• Eyes receive light
• Eyes send messages to
brain
• Brain interprets signals
as colors
• Long = red / short = violet
/ mixture of waves =
combination of colors
With opaque objects, how does
reflection and absorption impact
the color?
• Light hits opaque
object:
Some waves
reflected, see that
color
Some absorbed,
don’t see that color
How do we see a strawberry as
red?
• Red wavelengths reflected; other colors’
wavelengths absorbed
What makes something white?
• All colors’ wavelengths are reflected
What makes something black?
• All colors’ wavelengths are absorbed
What about color in non-opaque
objects?
• Transparent: Colorless in white
light because all light waves pass
through (transmit). Think of glass
window.
• Translucent: Shows color of
wavelength reflected or
transmitted; all others absorbed.
Think of stained glass.
How do pigments produce
color?
• Pigment = material that absorbs some
colors of light and reflects other
What has pigment?
• Pigment is in almost everything
What are two examples of
pigments?
• Melanin = pigment for skin
color
• Chlorophyll = plant color
What happens when pigments are
mixed?
• Each pigment absorbs
at least 1 color
• Mix pigments, more
colors are taken away;
color subtraction