Radiant Energy

- "LIGHT" is an electromagnetic (EM) wave that travels at the speed of light.


ALL light starts with a Vibrating Charged Particle.
Imagine holding a long rope that is tied off straight to a tree. If you move the rope quickly up and down you should notice a WAVE of energy that travels down the rope.

Similarly, if we were able to grab onto an electron and give it a wiggle AND a jiggle, we would generate a wave of energy that travels in every direction.

Try it yourself.



EM waves have both electric and magnetic fields.


Electromagnetic waves travel at the speed of light.


The speed of light is

300,000,000 meters per second! (in a vacuum)

or 300,000 kilometers per second

or 186,000 miles per second

Traveling faster than light speed is science FICTION.

Anything that travels at the speed of light IS light.

What is a "light year"?

Some think it is a speed. Some think it is a time.

It's the DISTANCE light would go after traveling for a year.

in English units

just under 10 trillion km !!!

about 6 trillion miles
exactly 9,460,730,472,580.8 km
exactly 5,878,625,373,183.6 miles



Let's put things into perspective a bit:

circumference of the EARTH
0.13 light seconds
distance to the MOON
1.5 light seconds
distance to the SUN
8.5 light minutes
distance to MARS

4 minutes (when at close orbit)

20 light minutes (when on opposite sides of the sun)

Proximus Centuri

(our 2nd nearest star)

4.3 light years

The galaxy is 100,000 light years across!

Imagine a star that is 1 million light years away, The light has been traveling through the vacuum of space for 1 million years in order to reach your eye. You are looking at 1 million year old light! It's a form of time travel.




Anatomy of an Electromagnetic wave

All EM waves move at the speed of light but each type of wave is a different size. We call it a WAVELENGTH .

A WAVELENGTH is the distance from one crest to the crest of the next wave. ( it works with troughs too)

The WAVELENGTH determines the type of light!

FREQUENCY- The number of waves that pass by a fixed point

One wave per second is called 1 Hertz

1,000 waves per second is 1 KiloHertz (AM)

1,000,000 waves per second is 1 MegaHertz (FM)

1,000,000,000 waves per second is 1 GigaHertz (cell phones)




Two important trends found with the EM Spectrum

1. As the WAVELENGTH decreases, the FREQUENCY will increase.

(think about the reverse too)

The range of longest to shortest wavelengths is called a SPECTRUM

The number of waves that go by is called its FREQUENCY.

in math class you might call a spectrum the "range" of something and you might think of frequency as the "mode"


EVERYTHING is moving at the same speed.

The people are small (short wavelength) so there are more of them (high frequency).

The jumbo jet is really BIG (long wavelength) so there is only one of them (LOW frequency).


2. As the WAVELENGTH decreases, the ENERGY will increase.

(think about the reverse too)

The more energy that it takes to make the waves, the greater the energy of the wave.






This one is so detailed its on Sheldon Cooper's wall...



low energy

High Energy

Type of Wave
Wavelengths are ABOUT the size of ...
BASIC information

AM Radio

the size of the school

(100's-1000's of meters)

measured in kiloHertz


RC car

garage door opener

TV and FM

the size of a tiger

(1-10 meters)

measured in MegaHertz

cordless phones

Microwave (Cellphones, XM)

the size of a bee

(centimeters to about a mm)

measured in GigaHertz

used in RADAR and cell phones

Perfect size to vibrate water molecules and use in "microwave ovens"


the size of a needle point

(millimeter - micrometers)


EVERTYHING that has heat emits Infrared

remote controls, night vision,

visible light

the size of an animal cell

(400-700 nanometers)

The ONLY portion that we can see with our eyes

Just imagine if we could see it all!


the size of a molecule

(10-400 nanometers)

causes "suntan" and sun burn which is the damaging of skin. There are NO safe ways to destroy skin cells.

bees CAN see this reflected off of flowers.

Perfect size to vibrate DNA and cause mutation.


(first "x-ray" photograph of Mrs. Wilhelm Röntgen 1896)

the size of an atom

(1 nanometer)

diagnostic medicine

Gamma Rays

and other cosmic radiation

the size of a nuclei and SMALLER!


.1 nanometers - ???

"Irradiate" food to rid it of bacteria


Most of the EM spectrum cannot be seen.


With all of those wavelengths, visible light is less than .000001% of the whole spectrum.

Here's another way to look at it...

If the entire spectrum was wrapped around the globe, the wavelengths of light that ARE VISIBLE would only be

40 centimeters of the whole world!

OR think about it in terms of money.


If the EMS was represented by

1 million dollars,

the human eyes could only see

1 PENNY's worth !!!


Electromagnetic waves travel in a straight line
In the vacuum of space, light travels straight and true. There is nothing to get in its way. Satellites are needed to send straight line communication around the sphere of the Earth.

When light travels through matter it will slow down and change direction slightly. This means that the cat (in the picture below) is looking at a fish that is really in a different location.

A convex lens will focus the image as the light crosses paths. Beyond the "focal point" the image is flipped upside down like the examples below.


Light can either be absorbed, reflected, or refracted

If ALL of the light passes through, the matter is called transparent.

If SOME light passes through the matter is called translucent.

If NONE of the light passes through, the matter is called opaque


The light we "see" must be reflected off of objects

Check out this interactive demo on the color we see!







Electro - magnetic