LIGHT 25.3
Chapter Twenty-Five: Light
25.1 Properties of Light
25.2 Color and Vision
25.3 Optics
Chapter 25.3 Learning Goals
Explain how basic optical devices
function.
Compare and contrast the
interactions of light and matter.
Distinguish between concave and
convex lenses.
25.3 Basic optical devices
Three useful optical devices are:
1. lenses
2. mirrors
3. prisms
25.3 Basic optical devices
A magnifying glass
is a converging lens
that can be used in
survival situations
to make a hot spot.
Mirrors can attract
the attention of
rescue teams from
great distances.
25.3 Four ways light is affected
by matter
All four interactions
almost always happen
together.
Green colored paper
absorbs some light,
reflects some light, and
is partly translucent.
Can you tell which
colors are reflected and
which are absorbed?
25.3 Four ways light is affected
by matter
A glass window is
mostly transparent,
but also absorbs,
scatters, and reflects
some light.
See if you can
identify where
certain colors are
absorbed and
reflected in this
picture.
25.3 Light rays
Reflection occurs when light bounces off a
surface and when light bends while
crossing through materials.
25.3 Reflection
There are two types of reflection; but not
all reflections form images.
Rays light that strikes a shiny surface (like
a mirror) create single reflected rays.
This type of reflection is called specular
reflection.
25.3 Reflection
A surface that is dull or uneven creates
diffuse reflection.
When you look at a diffuse reflecting
surface you see the surface itself.
25.3 Law of reflection
A ray diagram is an
accurately drawn
sketch showing how
light rays interact
with mirrors, lenses,
and other optical
devices.
25.3 Refraction
Materials with a higher index of refraction
bend light by a large angle.
The index of refraction for air is about 1.00.
Water has an index of refraction of 1.33.
25.3 Refraction
Vegetable oil and glass
have almost the same
index of refraction.
If you put a glass rod
into a glass cup
containing vegetable oil,
the rod disappears
because light is NOT
refracted!
25.3 Lenses
An ordinary lens is a
polished, transparent
disc, usually made of
glass.
The shape of a
converging lens is
described as being
“convex” because the
surfaces curve
outward.
25.3 Lenses
The distance from the center of the lens to
the focal point is the focal length.
Light can go through a lens in either
direction so there are always two focal
points, one on either side of the lens.
25.3 Lenses
For a converging lens, the first surface (air
to glass) bends light rays toward the
normal.
At the second surface (glass to air), the rays
bend away from the normal line.
Searching the Cosmos
Astrophysicist Dr. Hakeem
Oluseyi (Oh-lu-SHAY-ee) is
fascinated by stars. A
physics and space science
professor at the Florida
Institute of Technology,
he has invented several
new instruments to give
astronomers a closer look
at the cosmos.