Laser Beam: Tyndall Effect, Scattering, and RefractionElizabeth MorenoAward: Top 100
School: glenbard west high school In a truly pure solution, dissolved particles are too small to deflect light passing through it. Therefore, the beam of light is not visible. In suspensions, dispersed particles are large and settle out upon standing. However, dispersed particles of a colloid are intermediately sized and do reflect light. Colloidal particles disperse evenly throughout dispersion mediums of any phase without settling out upon standing. In this case, particles are suspended in liquids, and some of them qualify more as colloids than others. The Tyndall effect is in play, meaning there is a scattering of visible light by colloidal particles. This is similar to when a light beam is "seen" passing through fog, smoke, or dust particles in the air. In the vials to the left, the solutions are increasingly colloidal. The particles are just the right size to scatter red wavelengths of light more than others, causing the visible beam of light coming from the laser pointer. As the solutions become decreasingly colloidal, the light beam is less visible. 
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