Electromagnetic
Spectrum
Radiation – energy moving from a source as a
wave
Light is a combination of electric and magnetic
energy.
Light can behave as both a particle and a wave.
The particle is a packet of light called a photon.
Two main properties of light:
Brightness (intensity)
- amount of energy carried by light
- determined by the height
(amplitude) of the wave
OR
- the number of photons
Color
Color
Color of light is determined by its
wavelength (λ).
Wavelength – the distance
from crest to crest
Frequency – the number
of crests passing a given
point in a second (measured in cycles per
second OR Hertz -Hz)
Amplitude – distance from the center of the wave
to the crest or trough
Velocity (speed) of a wave:
The velocity of a wave can be calculated using
the formula:
V= ν λ
Where V = velocity
ν = frequency and
λ = wavelength
The speed of light is 3.0x10-8 m/s.
This is actually the speed of ALL wavelengths of
all of the different types of radiation- including
light.
Because the velocity is the same, as wavelength
increases, frequency decreases.
Electromagnetic Spectrum
The electromagnetic spectrum spans longer
and shorter than the visible spectrum.
Types of Radiation
Gamma Rays (γ)
- High Energy radiation- The “dangerous”
radiation from nuclear decay, nuclear reactors,
and bombs.
- Gamma radiation can be stopped by several
feet of concrete, or many inches (7-8 or so),
of lead.
X Rays
• X rays go through “stuff” such as skin, and
clothing. Depending on the density of the
“stuff” film is exposed in different amounts.
• From the following x-rays- you can see the
skin ( barely) bones ( quite well) and even
metal- (very clearly) as X rays do not pass
easily through very dense objects- such as
metal, etc.
Ultraviolet (UV) radiation
What is the most important source?
The Sun
What protects the earth from UV radiation?
The ozone layer
U.V. radiation is bad because it causes:
Skin cancer
Visible Spectrum
Red, Orange, Yellow, Green, Blue, Indigo, Violet
ROYGBIV
Red – longer wave length
Blue – shorter wavelength
White light is a mixture of all colors.
Infrared Radiation
Infra- beyond
Infrared is a larger wavelength than red.
We can’t perceive it, but some animals such as
snakes can.
Infrared radiation I.R. is used in remote control
devices and heat lamps.
This way McDonalds can cook a hamburger 4
hours ago, and keep it hot for you!
Microwaves
Microwave radiation has been used in
communication as well as …
Cooking popcorn!
Microwaves cause water molecules (in food) to
vibrate and thus heat up.
Radar
Radars send out a signal, it hits an
object and reflects back to the
sender.
Knowing that the signal travels at the speed of
light (really fast!) a computer can determine
how fast an object is moving based on the time
it takes for a signal to get back to the receiver.
“Stealth” planes use radar absorbing substances
on their surfaces, and lots of funky angles to
prevent radar signals from getting back to the
receiver, thus making it hard to detect.
Television
Analog signals
Use a typical electromagnetic radiation beamed
from a TV station to a tower, or a satellite,
then beamed to your rabbit ears antennae.
Radio waves
Radio waves come in a large range of sizes.
They can be produced by stars, galaxies, nebulae,
and black holes, therefore radio telescopes can
be used to study stars and galaxies.
• Several types of radio signals
• Shortwave- perhaps still used by amateur radio
operators
• FM radio - Frequency Modulation
• AM radio - Amplitude Modulation