Which equation describes the relationship between absorbance and transmittance?

The relationship between absorbance (A) and transmittance (T) in analytical chemistry is defined by a specific logarithmic equation. Absorbance is a measure of the amount of light absorbed by a sample, while transmittance is the fraction of light that passes through the sample relative to the incident light.

The correct relationship is given by the equation A = -log(T), which highlights that absorbance is related to the logarithm of transmittance. This means that as transmittance decreases (indicating more absorption of light), the absorbance increases. It creates an inverse logarithmic relationship: high absorbance correlates with low transmittance and vice versa.

In this context, the first option presented as T = I/Io describes transmittance as the ratio of the intensity of the transmitted light (I) to the intensity of the incident light (Io), which is a relevant definition but does not directly characterize the relationship between absorbance and transmittance.

Therefore, the equation that accurately expresses this relationship and links absorbance to transmittance through logarithmic operations is A = -log(T). Understanding this foundational principle is crucial for interpreting spectroscopic measurements in analytical chemistry.