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• When colloidal particles are present, some of the light is scattered and
the incident beam passes through with weakened intensity.
The scattering is known as the Tyndall effect
The path of light through the medium, made visible as a result of the
scattering is known as the Tyndall beam.
A sunbeam is an example of a Tyndall beam (the light being scattered by
Analysis of the scattering as a function of the angle provides valuable
information about the sizes and shapes of colloidal particles.
When these are single macromolecules, the technique is therefore useful in
determining molar masses. The proportion of incident light that is scattered increases with an increase in the
number and size of the particles.
The intensity of the transmitted radiation is given by
I = Ioe-τI ( 1) where τ is known as the turbidity, Io = intensity of the incident radiation, I = the length
of the light path through the scattering medium.
For a spherical p article w here ( r < << λ )
the intensity of the radiation scattered through an angle θ is given by (Rayleigh Eq)
I θ = [Ks r6 ( l + c os 2 θ)]/ λ 4 ( 2) The constan...
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