Part 1 – Electromagnetic
Light can be described using two different
models: the wave model or the particle
The wave model describes
light as transverse waves
that do not require a
medium to travel through.
Describe a transverse wave.
What type of wave does not
need a medium to travel?
Discussion: Observations that could not be
explained by the wave model…
The particle model assumes that light is
contained in small packets called photons.
Photons do not have mass, they are more
like bundles of energy.
Red Light vs. Blue Light
Wave Model & Particle Model
According to the
wave model, red
light should have
because it has a
why couldn’t it
off the metal
The Speed of Light
During a thunder storm, what would
happen first: you hear the thunder or you
see the bolt of lightning?
In a vacuum, all light travels at the same
speed called c : 3 x 108 meters/second
Light is the fastest signal in the universe
** You should memorize this number!! All electromagnetic waves travel at this speed.
Speed of Light
The speed of light depends on the
medium that it travels through.
What type of medium is in a vacuum?
Light travels slower
through slower through
a medium than it does
in a vacuum.
The quantity that measures how bright a light is,
or the amount of light that illuminates a surface,
is called intensity.
On which squares is the light most intense?
The electromagnetic spectrum (EM spectrum) consists of
light at all possible energies, frequencies, and wavelengths. It
includes radio waves, ultraviolet waves, visible waves, x-rays,
Our eyes can
detect light waves
light) to 700nm
(red light). This is
called the visible
Sunlight contains ultraviolet light (UV
UV light has higher energy and shorter
wavelengths than visible light.
UV light causes sunburns. Prolonged or
repeated exposure may lead to skin
UV Rays are good too…
Cause skin cells to manufacture vitamin D
for healthy bones and teeth.
Used in hospitals for cleanliness
Real World Applications p.403
X – Rays
the UV part of the
Used in taking pictures
of the inside of the
X – ray Passes through
low density objects but is
absorbed by high density
objects, like bones and
X rays can be harmful to
humans because they
can kill healthy body
cells, or turn them into
Protective lead aprons.
Infrared (IR) Light
than visible light.
IR light from the sun
or a lamp warms you.
IR light keeps
cafeteria food warm.
Given off by hot
objects as they cool.
Thermogram - A special IR film
that detects the amount of IR
radiation given off. It can identify
warm or cold areas of an object
or person. Large amounts = Red,
Small amounts = Blue.
IR sensitive binoculars enable
people to “see” objects in fog or
Radio wavelengths with
Microwave ovens in the
US use microwaves with a
wavelength of about 12
Microwaves are reflected
by metals, and go through
paper and plastic, but are
absorbed by water, fat,
Microwaves are also used to carry
Microwaves will create large currents of
electricity and can be harmful with people
wearing heart pacemakers.
Waves with the
are radio waves: AM,
FM, short-wave, and
AM vs. FM Radio
Vary amplitude Amplitude constant
Frequency constant: Frequency Varies:
535 kilohertz (535,000) - 88 megahertz (88,000,000) -
1605 kilohertz (1,605,000) 107.9 megahertz (107,900,000)
Good over long distances
AM travels longer distances than FM waves
because AM has a longer wavelength
Longer wavelength than radio
Reflect even better than radio
TV antenna or dish receives waves and
uses them to make electrical current
Radar waves are at the
upper limit of the radio
Radar systems use reflected
radio waves to determine
the distance to and from
objects. Air traffic controllers and police
officers both use radar systems
Part 2 – Reflection, Refraction,
Lenses & Color
All types of electromagnetic waves have
the same properties as visible light.
They can be reflected and refracted.
Reflected: Bounces off an object.
Refracted: Bends going from one
material to another.
Another Light Model
A light ray is a model of light that
represents light traveling through space in
a straight line.
Every object reflects some light and
absorbs some light.
Light rays can be drawn to show how light
is reflected off a surface.
Rough surfaces reflect light in many
directions… sometimes called a diffuse
Reflection: The return of light or sound waves
from a substance
Angle of Incidence = Angle of reflection
The bending of light waves as they pass from
one material into another
Θi = Θi
Θr = Θr r
As light enters a denser material it bends toward the normal
Index of Refraction
The ratio between the speed of light in a vacuum and the
speed of light in a particular substance
Glass 1.5 to 2.0
** The higher the index of refraction, the more the light will slow and bend.
A lens is a transparent object, usually
made of glass or plastic.
The lens is curved so that it changes that
direction of light.
The amount the lens is curved and the
lens material determines how much the
light will be refracted.
A lens that is thicker at the center than at the edges
Glasses for people that are far sighted
A lens thinner at its center than at the edges
Glasses for people who are nearsighted
Peepholes for doors
Some wide angle camera lenses
A spherical reflecting surface that constitutes a
segment of the interior of a sphere
A spherical reflecting surface that constitutes a
segment of the exterior of a sphere.
Makes objects appear to be further away because objects
look smaller when you look at them in your mirror
Different wavelengths of visible light correspond
to different colors.
Your brain interprets each wavelength of visible
light as a certain color.
Every object absorbs or
reflects visible light
The reflected light
waves enter your eyes,
your brain interprets
them as colors.
White light is the combination of all
A prism is a transparent block that can
separate white light into its component
Water in the air can act as a prism,
separating white sunlight into the colors of
A device that produces a beam of highly concentrated
light that is all one frequency or color
Light, flashlight, or the sun:
The light from these sources is usually a mixture
of colors at different frequencies and
Light waves are all jumbled and independent of
each other once they leave the source
They go everywhere and become scattered
Waves are all the same frequency and wavelength
Crests and troughs line up and amplitudes are the same
All waves move in the same direction from the source
Definition of: laser
(Light Amplification by the Stimulated Emission of Radiation)
A device that creates a uniform and coherent light that is very
different from an ordinary light bulb. Many lasers deliver light
in an almost-perfectly parallel beam (collimated) that is very
pure, approaching a single wavelength. Laser light can be
focused down to a tiny spot as small as a single wavelength.
Laser output can be continuous or pulsed and is used in a
myriad of applications. Gas lasers are used to cut steel and
perform delicate eye surgery, while solid state lasers create
the ultra-high-speed, miniscule pulses traveling in optical
fibers traversing the backbones of all major communications
networks. Light traveling in an optical fiber is impervious to
external interference, a constant problem with electrical
pulses in copper wire.
How Does It Work?
• A laser is an optical oscillator, which is made out of a solid, liquid or gas
with mirrors at both ends. To make the laser work, the material is excited
or "pumped," with light or electricity. The pumping excites the electrons in
the atoms, causing them to jump to higher orbits, creating a "population
• A few of the electrons drop back to lower energy levels spontaneously,
releasing a photon (quantum of light). The photons stimulate other
excited electrons to emit more photons with the same energy and thus
the same wavelength as the original.
• The light waves build in strength as they pass through the laser
medium, and the mirrors at both ends keep reflecting the light back and
forth creating a chain reaction and causing the laser to "lase.“
• In simple laser cavities, one mirror has a small transparent area that
lets the laser beam out. In semiconductor lasers, both mirrors often
transmit a beam, the second one being used for monitoring purposes.
Unit # 7 : Waves: Pretest Problems
All electromagnetic waves travel at ________ meters/second
The speed of sound @ 0 o C. is _________ meters/second
The speed of sound @ 30 o C. is _________ meters/second
The change in the speed of sound per change of 1 oC. is ____
The speed of sound @ 50 o C. is _______ meters/second .
The speed of sound is 380 meters/second .
The temperature is _______ o C.
In the summer time (speed of sound : 350 meters/second ) ,
how far could a sound wave travel in a day ?
Unit # 7 : Waves: Pretest Problems
On a cold winter day (0 o C.) you beep your snowmobile
horn .The sound bounces off a cliff and returns to
you in 4 seconds . How far away is the cliff ?
Three people are playing jump rope . One person shakes
the rope 12 times in 3 seconds . The speed of the
rope is 20 meters per second . How long is the
At 30 o C. a tuning fork has a wavelength of 5 meters .
What is the frequency of the sound it produces ?
The speed of a wave is 3.0 x 10 8 meters/second . The
wavelength is 3 meters . What is the frequency
of the wavelength ?