Electromagnetic Spectrum – Properties
Session Objectives
By the end of this session, students will be able to:
Ø Explain
the properties of Electro Magnetic waves
Ø Correlate
different components of Electro Magnetic spectrum with different Spectroscopic methods
Properties
of EM Waves
• All
matter contains charged particles that are always moving; therefore, all
objects emit EM waves.
• The
wavelengths become shorter as the temperature of the material increases.
• EM
waves carry radiant energy.
What is the
speed of EM waves?
• All
EM waves travel 300,000 km/sec in space. (speed of light-nature’s limit!)
• EM
waves usually travel slowest in solids and fastest in gases.
|
Material |
Speed (km/s) |
|
Vacuum |
300,000 |
|
Air |
<300,000 |
|
Water |
226,000 |
|
Glass |
200,000 |
|
Diamond |
124,000 |
What is the
wavelength & frequency of an EM wave?
• Wavelength=
distance from crest to crest.
• Frequency=
number of wavelengths that pass a given point in 1 s.
• As
frequency increases, wavelength becomes….
• Wavelength
(λ)= distance between
consecutive crests or troughs.
Units: meters (m)
• Frequency
(ѵ) = number of
wavelengths that pass a given point in 1 s. The SI unit of frequency is the
hertz (Hz)/ cycles per second (cps)
• As
frequency increases, wavelength becomes smaller.
• Wave
number (ṽ) is the number of waves per unit distance
• m-1
Can a wave
be a particle?
• In
1887, Heinrich Hertz discovered that shining light on a metal caused electrons
to be ejected.
• Whether
or not electrons were ejected depended upon frequency not
the amplitude of the light! Remember
energy depends on amplitude.
• Years
later, Albert Einstein explained Hertz’s discovery: EM waves can behave as a particle called a photon
whose energy depends on the frequency of the waves.
• Electrons
fired at two slits actually form an interference pattern similar to patterns
made by waves
What did
Young’s experiment show?
Electromagnetic
Waves
How they are formed
Waves made by vibrating electric charges that can travel
through space where there is no matter
Kind of wave
Transverse with alternating electric and magnetic fields
Sometimes behave as
Waves or as Particles (photons)
EMR and
Spectroscopy
|
Technique |
Type of Electromagnetic Radiation |
Type of Matter Observed |
Type of Interaction |
|
Ultraviolet-Visible Spectroscopy |
Ultraviolet and |
Electrons and |
Absorbance |
|
Infrared Spectroscopy |
Infrared radiation |
Molecular |
Absorbance (or |
|
Fluorescence Spectroscopy |
Ultraviolet and |
Electrons and |
Emission |
|
Nuclear Magnetic Resonance Spectroscopy (NMR |
Radiowaves |
Nucleus |
Resonance or |
|
Flame emission spectroscopy (Flame photometry) |
Ultraviolet and |
Atoms |
Emission |
|
X-Ray Diffraction Crystallography |
X-rays |
Electron |
Diffraction or |
|
Atomic Absorption and Emission Spectroscopy |
Ultraviolet and |
Atoms |
Absorption or |
|
ESR Spectroscopy |
Microwaves |
Free radicals |
Absorption |
Certain
terms used in spectroscopy
• Spectroscopy
• Spectrophotometry
• Spectrometer:
an instrument with an entrance
slit, a dispersing device, and one or more exit slits, with which measurements
are made at selected wavelengths within the spectral range, or by scanning over
the range. The quantity detected is a function of radiant power
• Photometer
an instrument used in
photometry, usually one that compares the illumination produced by a particular
light source with that produced by a standard source
• Spectrophotometer:
A spectrophotometer is a
combination of two instruments, namely a spectrometer for producing
light of any selected color (wavelength), and a photometer for measuring
the intensity of light.
SUMMARY
• Wavelength=
distance from crest to crest.
• Frequency=
number of wavelengths that pass a given point in 1 s.
• Wave
number (ṽ) is the number of waves per unit distance
• m-1
•
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