What is the difference between percent transmittance and absorbance

The reason why we prefer to express the law with this equation is because absorbance is directly proportional to the other parameters, as long as the law is obeyed. We are not going to deal with deviations from the law.

Now, suppose we have a solution of copper sulphate which appears blue because it has an absorption maximum at nm. We look at the way in which the intensity of the light radiant power changes as it passes through the solution in a 1 cm cuvette. We will look at the reduction every 0. The Law says that the fraction of the light absorbed by each layer of solution is the same. For our illustration, we will suppose that this fraction is 0. If we plot absorbance against concentration, we get a straight line passing through the origin 0,0.

Question : What is the significance of the molar absorbtivity, e? In words, this relationship can be stated as " e is a measure of the amount of light absorbed per unit concentration". Molar absorbtivity is a constant for a particular substance, so if the concentration of the solution is halved so is the absorbance, which is exactly what you would expect.

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Consequently, the absorbance can also be given in terms of the percentage transmittance:. According to Beer-Lambert law , the absorbance of light, as it passes through a solution, is directly proportional to the path length of light through the material and the concentration.

So, we can write,. This constant has a specific value for a given substance, provided the temperature of the substance and the wavelength of light passed through it are kept unchanged.

This is an extremely useful relationship which allows concentrations of unknown solutions to be found by measuring the absorbance of light through a sample. If we make a solution, allow light to pass through it and plot how the transmittance changes as we change the concentration of the solution while keeping the path length travelled by light unchanged , we get an exponential relationship between transmittance and concentration:.

Transmittance vs. However, if we calculate the corresponding absorbance values and then plot a graph of absorbance vs. Absorbance vs.