The Ray Model of
Light
Lesson 4
Light and Matter
• Light is represented as straight
lines called rays, which show
the direction that light travels.
• Ray diagrams are drawings that
show the path that light takes after
it leaves its source. Each ray ends
with an arrow to indicate the
direction of travel.
Light and Matter
• Ray diagrams can help explain why
the brightness of a light changes with
distance. The more rays that reach
your eyes, the brighter the object
appears
Light and Matter
• Ray diagrams are used to describe
what happens when light strikes an
object.
• Light travels in straight lines until it
strikes something.
• Materials have different properties
which affects what happens when light
strikes them
Light and Matter
• Transmit - Light passes through them.
Example: Clear glass
• Absorb – Light is absorbed by the
object and turned into heat
• Reflect – Light bounces off the object.
Light and Matter
The properties of materials can then be
further classified
• Transparent materials, such as clear
glass or clear plastic, transmit light
freely.
• Transparent materials absorb and
reflect very little light. Example: a
clear window
Light and Matter
Translucent materials transmit some
light, but not enough to see through
the material clearly. Example: A
frosted window pane. Some light can
pass through, but you cannot see what
is on the other side of the frosted glass
in any detail.
Light and Matter
• Opaque objects absorb and reflect
light, but they do not transmit it
Shadows
• A shadow occurs when an opaque
object blocks the direct light from a
light source
Shadows
• Ray diagrams can be used to show
1.How the size of the shadow depends
on the objects distance from the light
source
• A larger object will produce a larger
shadow
• An object closer to the light source
will produce a larger shadow
Shadows
Shadows
2. How the sharpness of the edges of a
shadow are depend on the objects distance
from the light source and the size of the
light source.
– The closer the object is to the light source
the fuzzier the shadow is.
Shadows
• Large light sources provide shadows
with fuzzy edges - penumbra
– This is due to the object only partially
blocking the light.
• The umbra is the part of the shadow in which
all light rays from the light source are blocked
– Point source (Small light sources) show
well defined shadows
TShadows
Drawing Light Ray
Diagrams of Shadows
1. Draw a line from the top of the
light source to the top of the
opaque object and continue onto
the wall
2. Draw a line from the top of the
light source to the bottom of the
opaque object and continue onto
the wall
Drawing Light Ray
Diagrams of Shadows
3. Draw a line from the bottom of the light
source to the top of the opaque object
and continue onto the wall
4. Draw a line from the bottom of the light
source to the bottom of the opaque
object and continue onto the wall
5. Label the umbra and penumbra
Examples
Reflection of light
• Even objects that do not reflect an
image still reflect light.
• Everything you can see in the room right
now is reflecting light.
Reflection of light
• When light rays reflect off a rough
or uneven surface, they do not
remain parallel but are scattered in
different directions, resulting in a
diffuse reflection. Because the
light is scattered, the rooms lighting
is even without bright spots.
Questions – Hand in
• 1. How does a transparent object interact with
light? K (1)
• 2. How does a translucent object interact with
light? K (1)
• 3. How does an opaque object interact with
light? K (1)
• 4. What is diffuse reflection? C (1)
• 5. Make two light ray shadow diagrams of
your choice. C (4)