Question

According to Beer’s law, the intensity of the emerging light from a solution depends on _________________ of the absorbing medium.
A) Length
B) Concentration of the solution
C) Molar absorptivity
D) All of these

Answer 1

Hint: Recall the expression given by Beer’s law. Beer’s law states that when a monochromatic light passes through a transparent medium, the rate of decrease in the intensity of the light with the thickness of the absorbing medium is directly proportional to the intensity of the incident light and the concentration of the solution.

Complete step by step solution:
Lambert first studied the behaviour of the monochromatic incident light on an absorbing medium. His law states that when a monochromatic light passes through a transparent medium, the rate of decrease in the intensity of the light with the thickness of the absorbing medium is directly proportional to the intensity of the incident light. But later on, Beer studied the effect of concentration of the coloured constituents in solution upon the light transmission or absorption. He gave Beer's law which states that the absorbance of the incident light is directly proportional to the concentration of the solution. On combining Lambert’s law and Beer’s law, we get a fundamental law which is known as Lambert-Beer’s law or simply, Beer’s law. The expression of the fundamental Beer’s law is:
$A = \varepsilon Cl$
Where, A is the absorbance, $\varepsilon $ is the molar absorptivity or molar absorption coefficient., C is the concentration of the solution, and l is the length of the absorbing medium or also called path length. Thus, we can conclude from the above expression of the Beer’s law that the intensity of the emerging light from a solution depends on-
- Length
- Concentration of the solution
- Molar absorptivity

Hence, option D is correct.

Note: The relation given by Beer’s law can be used to determine the concentration of the chemical species in a solution using a colorimeter or spectrophotometer. It should also be known that molar absorptivity determines how well a substance absorbs a particular wavelength. More is the molar absorptivity, the more probable the electronic transition is.