Transcript Document

General Properties of
Electromagnetic
Radiation
Lecture 1
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Electromagnetic radiation is looked at as
sinusoidal waves which are composed of a
combination of two fields. An electric field
(which we will use, in this course, to explain
absorption and emission of radiation by
analytes) and a magnetic field at right angle
to the electric field (which will be used to
explain phenomena like nuclear magnetic
resonance in the course of special topics in
analytical chemistry offered to Chemistry
students only).
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The classical wave model
The classical wave model describes
electromagnetic radiation as waves that have
a wavelength, frequency, velocity, and
amplitude. These properties of
electromagnetic radiation can explain
classical characteristics of electromagnetic
radiation like reflection, refraction,
diffraction, interference, etc. However, the
wave model can not explain the phenomena
of absorption and emission of radiation.
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We will only deal with the electric field of
the electromagnetic radiation and will
thus refer to an electromagnetic wave
as an electric field having the shape of
a sinusoidal wave. The arrows in the
figure below represent few electric
vectors while the yellow solid
sinusoidal wave is the magnetic field
associated with the electric field of the
wave.
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Wave Properties of
Electromagnetic Radiation
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Wave Parameters
1. Wavelength ()
The wavelength of a wave is the distance
between two consecutive maxima or
two consecutive minima on the wave. It
can also be defined as the distance
between two equivalent points on two
successive maxima or minima. This
can be seen on the figure below:
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2. Amplitude (A)
The amplitude of the wave is represented
by the length of the electrical vector at
a maximum or minimum in the wave. In
the figure above, the amplitude is the
length of any of the vertical arrows
perpendicular to the direction of
propagation of the wave.
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3. Frequency
The frequency of the wave is directly
proportional to the energy of the wave and is
defined as the number of wavelengths
passing a fixed point in space in one second.
4. Period (p)
The period of the wave is the time in
seconds required for one wavelength to
pass a fixed point in space.
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5. Velocity (v)
The velocity of a wave is defined as the
multiplication of the frequency times
the wavelength. This means:
V = 
The velocity of light in vacuum is greater
than its velocity in any other medium
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Since the frequency of the wave is a
constant and is a property of the
source, the decrease in velocity of
electromagnetic radiation in media
other than vacuum should thus be
attributed to a decrease in the
wavelength of radiation upon passage
through that medium.
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6. Wavenumber ()
The reciprocal of wavelength in
centimeters is called the wavenumber.
This is an important property especially
in the study of infrared spectroscopy.
 =k
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