When colloidal particles are present some of the light

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Unformatted text preview: um is said to be optically clear. • • • • • • 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 dust particles). 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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This note was uploaded on 10/25/2012 for the course CHEMISTRY 570.448 taught by Professor Billball during the Fall '10 term at Johns Hopkins.

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