Download Behavior of light

Chapter 16
Light waves do not follow
the same rules as other
forms of waves. Many
different models have been
used to describe its
behavior.

Wave Model of Light:




Light is an electromagnetic
wave made up of an oscillating
electric and magnetic field.
Light waves have transverse
motion.
Frequencies increase and
wavelengths decrease as we
move from red to purple.
Particle Model of Light





Light moves like an invisibly small stream of particles.
The particles travel in straight lines until they strike a surface.
Intensity (number) of particle strikes increase from red to purple.
Particles are not considered matter, but they behave like a stream
of matter particles.
Photon Model




Hybrid of wave and particle models.
Light is composed of particles called photons, and each photons
contains a certain amount of energy.
Color of photon depends upon the amount of energy it contains
(correlates to the frequencies of the wave model)
Even though
there are different
models of the
light waves, their
energies seem to
be proportional
no matter what
the model.


Electromagnetic
waves are
typically
arranged on a
spectrum
according to the
wave model.
Lowest to highest frequency:
Radio < Microwave < IR < Visible < UV < X Rays < Gamma Rays
Lowest to highest wavelength:
Gamma Rays < X Rays < UV < Visible < IR < Microwave < Radio
Radio Waves:

Uses:



Communication
RADAR
Microwaves

Uses:


Cooking

Communication via
Satellites
Infrared light

Uses:


Warmth

Night Vision
Equipment

Fire Detecting
Equipment
Visible

Uses:


Vision

Electronic projection
and imaging
Ultraviolet (UV)

Uses:


Disinfects tools

Medical detection
device

Forensics detection
device
Dangers:


Can mutate DNA
X-Rays

Uses:


Medical Imaging (hard
tissue)
Dangers:


Can mutate DNA
Gamma Rays

Uses:


Cancer treatment
Dangers:



Causes radiation
sickness.
Will mutate DNA

The speed of light (c) is 3x108 m/s (186,000
mi/s) in a vacuum.
Light slows as it passes
through a medium.




Light travels quickest in
clear or transparent
mediums (A).
Light slows considerably
in cloudy or translucent
mediums (B). Some
energy is absorbed or
reflected.
Light will not travel
through solid color or
opaque mediums (C).
Most energy is absorbed
or reflected.

Optics is the field of science that deals with the
propagation and behavior of light.
Reflection is the bouncing of a wave off of a boundary.

The law of reflection describes how waves reflect:


“The angle of incidence equals the angle of reflection.”
Angle of Incidence
– the angle between
the incoming ray
and the normal.
Angle of Reflection
– the angle between
the outgoing ray
and the normal.
Normal – an
imaginary line 90o
(perpendicular) to a
surface.

Entire images can be reflected off of surfaces
that are smooth, allowing the angles of
reflections to be consistent.

Mirrors are tools used
to create images
through reflection.

There are 3 types of
mirrors:
 Plane (Flat)
 Concave
 Convex
Two types of images can be
created with mirrors:

Virtual images form at a
point where light rays
cannot exist (ex. behind
mirror).


All mirrors can produce virtual
images.
Real images are formed by
many light rays coming
together in a specific
location (projection)


Only concave mirrors can make
real images.
Refraction is the
bending of waves as
they pass from one
medium to another.


Shaped glass tools
called lenses are
used to bend waves a
specific amount
through refraction.
There are two types of
lenses:

Convex Lens

Converge light (beams
converge behind it in a central
focal point)
Produce real or virtual images.
Uses: magnifying glasses, our
eyes



Concave Lens



Diverge light (beams spread
outward)
This type of lenses can only
create a virtual image.
How do we see?

1.
2.
3.
4.
5.
Light waves reflected from an
object travel toward the eye.
The cornea bends and focuses
light towards the lens.
The lens refracts light and
focuses it on the retina.
Specialized cells called rods
detect light intensity while cones
detect color.
Signals from the retina travel to
the brain from the optic nerve.

Different colors come
from white (sun)
light.
Each of these colors
has its own frequency,
wavelength, and
energy.
 Our eyes can detect the
following wavelengths
in the electromagnetic
spectrum: λ= 400 nm
(violet light) – 700 nm
(red light). (ROYGBIV)


A prism is a
transparent block with
a triangular crosssection that can
separate white light
into all of its colors.
 This phenomenon is
called dispersion
and is caused by the
differences in the
refractive angles of
different colors of
light.

Rainbows are formed by natural dispersion
through water droplets in the atmosphere.

There are three primary colors of light: red,
blue, and green.
Objects that create
their own light can
produce different
colors using the
additive method.


These items appear
black unless they are
producing light.
Objects that cannot produce their own light
must reflect light in order for them to have a
color.


Pigments absorb specific wavelengths of light. The
reflected wavelengths combine to give an object
color.
This is called
subtractive color.



Objects that are white
contain no pigment and
reflect all 3 primary colors
of light.
Objects that are black
have pigments that
absorb all 3 primary
colors of light and do not
reflect any wavelengths.