1. If the concentration of the solution is more than 10-2M (0.01M) in that case the linear relation is not obtained, when we plot a graph of Absorbance V/s concentration. That means law is deviated.
2. The molar extinction coefficient ε depends on the refractive index of absorbing medium. If the initial concentration of the absorbing medium is greater than 10-2 M then refractive index changes and so ε changes. If the concentration is less than 0.01M the refractive index does not change with the concentration and so the ε does not changes and law holds true.
3. The low also fail, if the absorbing spices react with the solvent i.e. either association or dissociation takes place. $$ \underset { Orange }{ { Cr }_{ 2 }{ O }_{ 7 }^{ -2 } } + { H }_{ 2 }O \Longrightarrow 2{ H }^{ + } + 2\underset { Yellow }{ { CrO }_{ 4 }^{ -2 } }$$
4. The law is also deviated if the monochromatic light is not used.
5. Change of temperature also leads to deviation of Beer-Lamberts Law.
6. The deviation may occur if the width of the instrument is not proper.
7. The deviation also occurs in the instrument where filters are used because with filters we do not get monochromatic light.
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