Final answer:
A colorimeter measures the amount of light at a given wavelength that is absorbed by a liquid, which is significant for analyzing the concentration of substances in the solution.
Step-by-step explanation:
A colorimeter measures the amount of light at a given wavelength that is absorbed through a liquid. This is important in determining the concentration of a substance within that liquid. When white light passes through or is reflected by a substance, a specific portion of the light spectrum is absorbed, leaving the complementary color visible to the observer. For example, if a substance absorbs light at the 420-430 nm range, it appears yellow because this is the complementary color. Instruments like spectrophotometers are used for measuring light absorption, where a single wavelength of light passes through the sample, and the optical density or turbidity can be analyzed against a control to measure the cell density in a solution, such as a bacterial cell suspension.