Why does water appear white when it falls from height?
AKSHAY POLA
Bidar, Karnataka
Water falling from a height appears white due to a phenomenon called non-selective scattering.
When water falls from a height with high velocity, lot of tiny water droplets are formed around the falling mass of water due to the bombardment of water with the rocks. These tiny droplets are about 100-1000 times bigger in size when compared with the wavelength of visible light which human eyes can see. (The visible range to which human eye is sensitive is about 0.4-0.7 micro metre, 1 micro metre = 10 raised to the power -6 metre).
The light coming from the sun which the humans can see has three primary colours red, green and blue mixed in it. When light rays are incident over the water droplets, they scatter the entire visible range equally in all directions.
When the three primary colours red, green and blue are mixed in equal proportions, they produce white colour. Hence, the colour we see after scattering by the water droplets is white.
When water falls with a low velocity, very less or even no such tiny droplets are formed around the falling water and hence no scattering takes place. Hence we do not see white falling water at those times.
ESWAR R.
Research Scholar
Indian Institute of Science
Bangalore
