Transcript Chapter 15 Notes

AGENDA
Review Class Policies
Turn in Chapter 14 Homework
Chapter 15 Notes
Finish Ch. 15 Homework, due today.
Work on Semester Review
Optics
• Optics is the study of the behavior of light.
• Optics deals with the collection and use of
light to create images.
• Optical devices are used to change the
direction light
• Lens: bend light so that it comes together
• Mirror: reflect light
• Prisms: to bend and separate light
Light Rays
• A light ray is a imaginary arrow
that follows a single beam of
light, this simplification allows us
to analyze where light travels
• When we see an object, every
point on the object reflects many
rays of light in all directions. As
a result, the rays comes from
objects.
Images
• The light rays all come from the object and come together
to form the image.
• Objects are real physical things that give off or reflect
light rays.
• Images are “pictures” of objects that are formed in places
where the light rays from the object meet. The image
might not represent the object as it truly is.
• The focus is the place where all the light rays from the
object meet to form the image.
Optical Systems
• Most optical devices have two important functions: collect
light rays and bend light rays to form an image.
• Lens is a special shape clear solid material that use
refraction to create an image.
• Refraction: bending of light as the light crosses a
boundary between two different substances.
• Mirror reflects rays of light so that they change their
path.
• Reflection happens when objects or waves “bounce”
off a surface.
Reflection and Mirrors
• The law of reflection says
that light rays bounce off a
reflected surface at the same
angle at which they arrive.
• The angle of incident equals
the angle of reflection
relative to the normal.
• Normal is a line
perpendicular to the
surface.
Refraction and Lenses
• When light crosses
the boundary
between two
different materials
the rays bend.
• A lens is a curved
piece of glass that is
used to bend light
rays to a single
point called the
focal point.
Types of lenses
• There are two types of lenses: converging lenses
and diverging lenses.
• Converging lenses (convex lens) bend light
toward the focal point.
• Diverging lenses (concave lens) bend light
away from the focal point
Ray Diagram
• A ray diagram traces several light rays as they go
through the system.
• The rays come from the object and are bent or
bounced as they encounter a lens or a mirror.
• The location where the bent or bounced rays meet
is the location of the image.
The Human Eye
• The cornea and lens focus light so
that an image forms on a special
membrane on the back of the eye
called a retina.
• The rod and the cone cells sense
the image and transmit them via
the optic nerve to the brain
Forming an Image
• The lens focuses light on the
retina at the back of the
eyeball.
• The image is INVERTED
(upside down)
• Small muscles around the lens
stretch and change the shape
of the lens. This allows you to
focus on objects at different
distances.
Vision Problems
• As you get older the lens loses
some of its flexibility. As a
result, as you get older your
vision will get worse.
• Nearsighted individuals eyes are
too long, as a result the image
focuses before the retina.
• Farsighted individuals eyes are
too short, as a result the image
focuses outside the eye.
LASIK
• LASIK is a procedure that permanently changes the
shape of the lens of your eye.
• Pulses from a computer controlled laser vaporize a
portion of the lens.
• Problems: thins cornea, increases halo vision and dry
eyes
• Who can’t have it: under 18, pregnant, participate in
contact sport, some illnesses, or had vision change in
the last year
• Cost most medical plans will not cover the
procedure. Typically costs about $1000 an eye.
Optical Illusions Optical Illusions
• The image that our brain produced is always
based upon the assumption that light travels in
a straight line.
• An optical illusion is where the brain interprets
an image to be something that it is not.
Refraction
• When light passes from one
medium into another medium
it is bent.
• Goes from air to glass the light
is bent toward the normal (B)
• Goes from glass to air the light
is bent away from the normal
(C)
Internal Reflection
• If the angle is big enough the light is reflected from the
surface instead of being refracted. This is called the
critical angle.
• If light approaches the surface greater than the critical
angle, it reflects back. This is called internal reflection
Fiber Optics
• Fiber Optic material is a thin
glass tubes that light travel
through to transmit
information.
• A light pipe traps light by total
internal reflection. The light
always approaches the wall at
angle greater than the critical
angle.
LASERS
• When energized the electrons in a laser move to
a higher energy level.
• Like “glow in the dark” material the electrons
return to a lower energy level producing a beam
of light.
• This beam of light is at a SINGLE frequency
REMINDERS
• Study Session for Benchmark Test on Monday
after school in Room W214.
• Open Book Test for Ch. 14 & 15 on Tuesday.
• Benchmark Next Thursday.