What is the relationship between absorbance and transmittance in a spectrophotometer?

The relationship between absorbance and transmittance in a spectrophotometer is best described as logarithmic. In this context, absorbance is defined mathematically as the negative logarithm (base 10) of the transmittance (T), which is the ratio of the intensity of transmitted light (I) to the intensity of the incident light (I0). This can be expressed using the formula:

[ A = -\log(T) ]

This means that as the transmittance decreases (meaning less light passes through the sample), the absorbance increases. Specifically, a higher absorbance indicates that more light has been absorbed by the sample, while a lower transmittance indicates that less light is being transmitted. This logarithmic relationship allows for easier interpretation of data and is fundamental in quantitative analysis in spectrophotometry.

Understanding this relationship is crucial for accurately interpreting results in biochemical assays, where concentration measurements are often derived from absorbance readings. Therefore, the correct answer reflects the true nature of how absorbance is calculated and directly relates to the amount of light transmitted through the sample.