ElectroMagnetic
Radiation Spectrum
The basics about light and waves
Breakdown:
1.) Terms to Know
2.) What is the E.M.R. Spectrum?
3.) How does light travel?
4.) Characteristics of a wave and light
Terms to know:
1.) Radiation - process of emitting radiant energy (light) in the forms of
waves and particles
2.) Electron - subatomic particle of atoms with a negative charge and the
least mass; usually found orbiting the nucleus
3.) Magnetic fields - lines of force that connect the positive and negative
areas of a magnetic body
4.) Waves - movement of energy through a medium or empty space in the
pattern of a sine wave
5.) Spectrum - a continuous sequence or range; in this case, the
wavelengths of light
The E.M. Spectrum
- The Electromagnetic spectrum is the full
range of wavelengths that light can travel in
The E.M. Spectrum
- light, or radiation, travels at a constant
speed in a vacuum
c = ~300,000 km / s
- there are many different types of light, but
they all share the same speed
Visible, Ultraviolet (UV), Infrared (IR), X-rays, Microwaves,
Gamma Rays, and Radio Waves
How does light travel?
- Light, depending on how you study it, can
have the properties of waves or particles
o The EM spectrum breaks down the types of
light based on wavelength so we will focus on
waves
* Light is special in that its waves do not
require a medium to travel through
ex: there is no sound in the vacuum of space because there is no
matter for it to travel through
Waves
- 2 types of waves:
Transverse and Longitudinal
- Even though matter may be moving (up, down, and all
around), it does not travel with the waves, only energy
is being passed along. This is true with all waves.
- Wavelength = distance between two crests or two troughs
(in the case of longitudinal waves, the distance between
two areas of compression)
 measured in SI units (meters)
Longitudinal Waves
•Waves that travel parallel
to the direction of motion
•Made up of compressions
and rarefactions in the
medium that they are
traveling in
•Examples: sound waves
and s waves for
earthquakes
Transverse Waves
•Waves that travel
perpendicular to the
direction of
displacement
Examples: Light, p waves
for earthquakes, Ocean
waves
*Misconception
- As you should have seen, Radio Waves are
a type of light and therefore are not sound.
Sound waves = Radio waves !
- You may ask: But I hear sound from my
radio, how is this possible?
- Because of the nature of light, sound
information can be encoded in Radio waves
and later extrapolated back out as sound
.... how this is done is a topic for another time
Characteristics of a Wave
There are 4 basic components to any
transverse wave such as light:
1. Amplitude
2. Frequency
3. Phase
4. Polarization
1.) Amplitude
- Amplitude is the total displacement of a
wave.
o In simple terms, it is the distance from the
middle of a wave to its peak
2.) Frequency
- Number of crests (or wavelengths) passing
by per second
- Measured in Hertz (Hz), meaning cycles
per second
- Equals the inverse of the time it takes for
one wavelength to pass by:
f=1/t
3.) Phase
- Phase is the initial
angle of a sinusoidal
function at its origin
- If two waves are the
same or similar in
phase, they will add
together
- If they offset enough,
they will subtract
4.) Polarization
- Polarization is the orientation of oscillations
in the plane perpendicular to a transverse
wave's direction of travel
o Different polarizations are cause by the electric
and magnetic fields being out of phase from one
another
- Possible Polarizations:
1. horizontal
2. vertical
3. circular
4. elliptical
Other properties of light:
Because of lights characteristics and physical
nature, light has some other interesting
properties:
● Diffraction
● Refraction
● Scattering
Diffraction of Light:
Diffraction of light is the “interference” of its
waves when it encounters an opening or an
obstacle.
- Seen when the obstacle or opening
matches up closely with the waves
wavelength
- Longer wavelengths get diffracted more
than shorter wavelengths
Diffraction of Light: (cont.)
The effects of diffraction are most “easily”
examined via the single-slit and double-slit
experiments
Based on the size of slits used in comparison
to the wavelengths of light, different
patterns of interference result
1x
5x
Refraction of Light:
Refraction is the bending, or change in
direction of light as it passes from one
medium to another
- The secondary medium has a different
refractive index from the first
Refraction of Light: (cont.)
If you have ever looked at an object
underwater from above, you have witnessed
refraction. Because light gets bent as it
changes mediums from the air to the water,
the image you see becomes “distorted.”
Refraction of Light: (cont. x 2)
- A prism works based on this concept. As
light enters a prism, the light gets bent as it
passes from one medium to the other. Prisms take it a step further and bent each
wavelength of light differently
● This spreads the light out into a
rainbow of color as you may have seen.
o The shorter wavelengths bend more
than the longer.
Scattering of Light:
Light scattering is the deflection of an
incident beam of light off any irregular
portion of the medium in which it is passing
through.
● Light scatters off of any surface
generally speaking, and the type of light
being scattered, or reflected, is the
color in which you see.
Why is the sky blue?
The atmosphere is a collection of gases that
is, for the most part, evenly distributed. As
light passes through it, light randomly
strikes small particles and molecules
suspended in the air column. Because of
this, light gets scattered in all directions.
● Shorter wavelengths are more easily
scattered, so blue light gets scattered
more.
What about dusk and dawn...
You may notice when the sun rises and sets,
the sky is no longer “blue” but instead more
of a yellow/red hue. During these times,
sunlight enters the atmosphere at a more
extreme angle and must pass through more
atmosphere to reach your eyes. By this time,
all or most of the shorter wavelengths have
been scattered leaving only the longer
wavelengths.
If shorter wavelengths scatter
more easily...
Then why isn’t the sky violet?
- There just isn’t enough violet light
being emitted from the Sun. The sun
because of its temperature gives off
much more blue light therefore it is
more prevalent.