Electromagnetic Spectrum
Range of Behavior
 Electromagnetic waves are
characterized by their
wavelength or frequency.
 c 
• Linked by the speed of light
 The frequency is associated
with an energy.
• High frequency is high energy
E  h  hc 
 The common unit is the
electron-volt (eV).
• Work done by 1 V potential on
one electron
hc = 1.240 keV nm
Electromagnetic Radiation
 Traditional upper boundaries for types of EM radiation:
Radio waves
Microwaves
Infrared
Visible light
Ultraviolet light
X-rays
Gamma rays
 (m)
1
110-3
0.7510-6
0.410-6
1.210-8
1.410-11
 (Hz)
E (eV)
3108
1.2410-6
31011
1.2410-3
41014
1.65
7.51014
3.1
2.41016
1102
31019
1.2105
(highest energy)
Radio Waves
 Radio waves primarily come
from the oscillation of currents
in conductors.
 A 1 MHz frequency has an
energy of 6.6 x 10-28 J.
 The long wavelengths travel
easily and are not interfered by
atoms.
• Except conductors
Microwaves
 Microwaves are very short
wavelength radio waves.
 Microwaves are associated
with the vibrations of some
atoms and molecules.
 Water molecules act as a
dipole.
• Motion increased by
microwaves
• Causes heating
Radiation from Heat
 Heated objects give off
electromagnetic waves.
• Higher temperature has more
radiation
 A hot object gives off a
spectrum of frequencies.
intensity
low
energy
high
energy
• Shifts based on temperature
 This is called blackbody
radiation
frequency
Infrared
 Wavelengths longer than
visible light are called infrared
rays.
• Come from warm objects
 Molecules are heated by
infrared waves.
• Radiant heat
Visible Light
 Visible light is radiation in a
narrow band of wavelength.
• 400 nm to 800 nm
• Narrower ranges are colors
 Corresponds to maximum
output from the Sun.
intensity
low
energy
high
energy
 Many atoms and molecules
have specific behavior at
unique frequencies of light.
frequency
Ultraviolet
 Ultraviolet rays have shorter
wavelengths than visible light.
• Higher energy
• Often with visible light
 Some molecules absorb
ultraviolet and reemit visible
light.
• Fluorescent light
X-Rays
 X-rays are associated with
energetic transitions in atoms.
electrons
target
 Continuous spectra result from
electron bombardment.
x-ray
 The short wavelength x-rays
can penetrate materials.
• Stopped by dense atoms
Gamma Rays
 Gamma rays are photons
associated with nuclear or
particle processes.
• Energy range overlaps: soft
gamma equals hard x-ray
g
e
e
Z
 Acceleration of a very
energetic charged particle
gives x-rays and gamma rays.
• Called bremsstrahlung
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