Spectrum of Transmitted Light

A diffraction grating is used to show the spectrum of the light that is not scattered by the milk suspension.

Discussion

Before milk is added to the water in the container, the light striking the reflecting screen has the full spectrum of colors. After milk is added, the light that passes through the suspension of milk micelles without being scattered is primarily at the red end of the spectrum. This confirms our earlier, more qualitative observations and conclusions about what wavelengths of light would not be efficiently scattered by milk in water (longer wavelengths - those at the red end of the visible spectrum), given the approximate size of milk protein micelles (about 100-200 nm, much smaller than the wavelength of light in the red part of the spectrum, roughly 650-700 nm).