For absorbance measurements, the optical density (O.D.) is a logarithmic measurement of the percent transmission (%T) and it can be represented by the equation, A = log10 100 / %T. That means a sample with: 1 O.D. allows 10% of light to be transmitted through the sample.

We can say that optical density is directly proportional to refractive index and inversely proportional to speed of light for that given medium. Complete Answer: Absolute refractive index is defined as the ratio of speed of light in vacuum to that in a given medium.

The overall increase of refractive index with increasing mass density is evident from the figure. The refractive index increases linearly with mass density when the mass density is much less than 1 g cm – 3 , but the linearity disappears for dense materials such as liquids and solids.

Optical density (OD) is used as a rapid proxy measurement of suspended biomass concentration. In fact, OD measurements are the most common measurement used in microbiology laboratories to assess microbial growth.

The optical density or absorbance of a material is a logarithmic intensity ratio of the light falling upon the material, to the light transmitted through the material: (5.76) where I0 and I1 are the intensities of the incident and transmitted lights, respectively.

The equation to be used (Beer-Lambert Law) is: A = E l C ; where A is the absorbance; C is the concentration and l is the cell’s width, E (epsilon coefficient) and its unit is mol/dm3.

The two main factors that affect absorbance are concentration of the substance and path length. Relation between concentration and absorbance: Absorbance is directly proportional to the concentration of the substance. The higher the concentration, the higher its absorbance.