Electromagnetic Radiation (EMR)
•Electromagnetic radiation is does not need a
medium to travel through, this is what really
makes it special.
•EMR displays wave properties and is made
up of two alternating fields, and electric field
and a magnetic field
•Applet
•This can be a little difficult because EMR acts
as a wave, but has no medium, only changing
fields which transfer energy
Electromagnetic Spectrum
• The electromagnetic spectrum describes all of
the different types of light
• EMR spectrum
• There are many trends found on the EMR
Spectrum including f, λ, and energy
The visible spectrum
Radio Spectrum
The speed of light
• The speed of light is thought to be the
universal speed limit, 3 X 108 m/s or 186,000
miles/second in a vacuum
• Light travels slower in other mediums
• It has its own constant c
• E=mc2
• One of the early experiments to determine
the speed of light was the Michelson-Morely
experiment
Absorption of light
• As you may know, when an atom is excited, its
electrons jump to an “excited state” when they
relax, they give of light.
• You can excite an atom by heating it, or having it
absorb an electron
• When it drops back to ground state, it gives off a
“photon of light”
Microwave Cooking
• You can also do the reverse, you can make
something hot by bombarding it with light
• Certain bond lengths absorb certain types of
EMR
• Microwave cooking applet
Light absorption
Duality of light
• Light behaves as a wave but it also behaves as
a particle or “photon”
• A photon can be thought of as a packet of
energy, or a particle of light
• Light acts like a wave or a particle depending
on the experiment you are doing
• This is confusing stuff, and at this level we
have to just accept it
Polarization of light
• The plane of natural
light spins as it
propagates
• When it reflects off of a
horizontal surface, the
plane tends to have
vibrate in one direction
• You can use Polaroid
lenses to filter out glare
Snell’s law is refraction
• When light travels through the interface from
a less dense medium to a more dense medium
it bends toward the normal
• When light travels through the interface from
a more dense to a less dense medium it bends
away from the normal
• The normal, is a line drawn perpendicular to
the boundry between the two materials
Snell’s law
Bow fishing
Why its hard to shoot a fish!
Lenses
Critical angle
• The critical angle is
when the light no
longer passes
through a material
and bounces off
Mirrors
• Mirrors reflect light
• The angle of incidence always equals the angle
of reflection
Convex mirror
Concave mirror
Rods see black and white, cones see color
Color
• White light contains all of
the colors of the visible
EMR spectrum
• In other words, white is
the absence of color
• Black is the absence of
light
• Newton’s color wheel
How we see something
• In order for us to see something that’s yellow a
couple things must happen
– The object must be illuminated by light that contains
yellow light
– The light must be reflected/scattered by the object and
some light must end up on our retina
– The color yellow must be the only one reflected
– So for an object to be yellow, it must absorb all other
colors except yellow that are shinning on it
Additive/subtractive colors
• When you add two or more different colors in
a source of light, our brain interprets it as
being a completely different color
• Applet colored light and filters
• Applet additive light
• Pigments added to something like white paint
don’t add colors, they subtract colors