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Beer lambert Law
- 1. TThhee BBeeeerr ––LLaammbbeerrtt LLaaww
- 2. The Beer –Lambert Law • When a monochromatic light of initial intensity Io passes through a solution in a transparent vessel, some of the light is absorbed so that the intensity of the transmitted light I is less than Io .There is some loss of light intensity from scattering by particles in the solution and reflection at the interfaces, but mainly from absorption by the solution. • Therelationship between I and Io depends on the path length of theabsorbing medium, l, and the concentration of the absorbing solution,c. These factors are related in the laws of Lambert and Beer
- 4. Lambert’s law • When a ray of monochromatic light passes throughan absorbing medium its intensity decreases exponentially as the length of the absorbing medium increases.
- 5. Beer’s law : • When a monochromatic light passes through an absorbing medium its intensity decreases exponentially as the concentration of the absorbing medium increases.
- 7. Transmittance: • The ratio of intensities is known as the transmittance (T) and this is usually expressed as percentage
- 8. Extinction • If logarithms are taken of the equation instead of a ratio then
- 9. • The expression log10 Io/I is known as the extinction (E) or absorbance(A). The extinction is some times referred as optical density. • Therefore • A (or) E = k cl • where k is molar extinction co-efficient for the absorbing material atwave length l, c = molar concentration of the absorbing solution,l = path length in the absorbing material in cm.
- 10. • If the Beer- Lambert law is obeyed correctly and l is kept constant, then a plot of extinction against concentration gives a straight line passing through the origin • Extinction, E=log10 Io/I
- 11. Transmittance
- 12. Extinction