Transcript Electromagnetic Spectrum Powerpoint File

Electromagnetic Waves
• Waves of energy emitted from any accelerating charges
• Any object that is above absolute zero emits
electromagnetic waves
• The entire range of possibilities is called the
“Electromagnetic Spectrum”
• Still confused? Then click What are electromagnetic
waves?
• To learn about the wavelength of photons click to the
next slide. To move onto the EM spectrum click
Electromagnetic Waves
• Wavelength is :
c
 
f
Where,
c is the speed of light (3 x 108 m/s in a vacuum)
λ is the wavelength in meters
f is the frequency in Hertz
What is this “photon” term you’re
throwing in there?
• A photon is a bundle (quantum) of light
• A photon has energy equal to
E  h
Recall that
h is Plank’s constant
ν is the frequency of the radiation (wave)
What does a photon do?
• Both magnetic and
electric forces involve
the exchange of
photons
• The photon has zero
rest mass, but has
momentum, can be
deflected gravity, and
can exert a force
TYPES OF ELECTROMAGNETIC
WAVES
GAMMA RAYS
• Emitted from the nuclei of
atoms during radioactive
decay or during highspeed collisions with
particles.
• Ionizing
• Used in cancer treatment
and for sterilization
Sources: Cobalt 60, the
inner core of the sun
X-RAYS
• Emitted when an electron
moves from certain excited
states back down to its
ground state, or when an
electron that is moving very
quickly is suddenly stopped
• Two groups - long
wavelength (soft x-rays) and
shorter wavelength (hard xrays)
• Used for radiography (x-ray
photography) and to look at
materials in industry for
defects
• Sources: emitted by heavy
atoms after bombardment by
an electron
ULTRAVIOLET
• Above the color violet
• Three groups - UV A, UV
B, and UV C.
• “A” type: longest
wavelength; least
harmful
• UV B and UV C are
absorbed by DNA in
cells
• Used by the body to
produce vitamin D, to kill
bacteria on objects, and
for sun tanning
• Sources: Ultra hot
objects 5000°C or more
VISIBLE LIGHT
• White light:
combination of all
the colors
• Rainbow: example
of white light that
has been
separated into a
continuous
spectrum of colors
• The names of
colors are assigned
in order of their
wavelengths
• Used for
communications
(fiber optics)
• Sources: very hot
objects
Color
Wavelength interval Frequency interval
red
~ 625 to 740 nm
~ 480 to 405 THz
orange ~ 590 to 625 nm
~ 510 to 480 THz
yellow
~ 565 to 590 nm
~ 530 to 510 THz
green
~ 520 to 565 nm
~ 580 to 530 THz
cyan
~ 500 to 520 nm
~ 600 to 580 THz
blue
~ 430 to 500 nm
~ 700 to 600 THz
violet
~ 380 to 430 nm
~ 790 to 700 THz
INFRARED
• Thought of as heat but is
not always
• Far infrared energy is
heat energy.
• All objects that have
warmth radiate infrared
waves
• Easily absorbed and reradiated.
• Used in remote
controls, surveillance,
therapy of muscles
• Sources: Humans, the
sun
MICROWAVES
• 1 mm-1 dm in length
• Absorbed by water
molecules – how
microwave ovens heat
food
• Used in
telecommunications and
power transmission
• Sources: electric circuits,
many stars, microwave
ovens
RADIO WAVES
• 10 cm- 100,000+m in
length
• Only cosmic waves the
reach the surface of
the Earth
• Cause of noise
• Divided into smaller
frequency dependent
groups called bands
• Used
for communications
• Sources: transmitters
and sparks from
motors
Polarization
• Electric and magnetic fields which make
up wave have preferred direction
• Can be horizontal, vertical, circular, or
elliptical
• Most radio emission is unpolarized
• To learn more click here
Polarization
y
Electric Field
Electromagnetic Wave
Wave
Magnetic Field
x
Horizontal Polarization
Vertical Polarization
y
y
E
x
z
x
E
z
Why Do We Care About Radio
Waves?
• Gadgets- cell phones, microwaves, remote
controls, garage door openers
• Science- radio astronomy, atmospheric
research