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The Tyndall effect in colloids can be demonstrated by passing a beam of light with a high degree of coherence, like that originating from a laser pointer, through the colloid.
A beam of light passing through a medium that does not have any suspended particles that cause the light to disperse is invisible. For the beam of light to become visible, the photons that constitute the beam have to be deflected by suspended particles in the medium it is traveling through. As a colloid consists of particles that can play this role, a beam of light from a laser pointer passing through it is visible.
The link below shows a laser beam passing through a clear solution and through a colloid. The beam is not visible as it passes through the clear solution but as it enters the colloid it becomes visible.
John Tyndall studied the phenomenon now know as the Tyndall effect in the mid 1800's. The Tyndall effect is demonstrated by shining a beam of light into a solution and observing the scattering of the light. This occurs in colloids because a colloid is a suspension in which undissolved particles are present. These particles will reflect and deflect photons of light which hit them. The random nature of the reflections causes a cohesive beam of light to diffuse as it penetrates the colloid, with some of the light photons reflected directly back toward the source.
The Tyndall effect explains why we see red and orange colors in the sky at sunset and sunrise, why clouds appear to be white, and why automobile headlights do not penetrate well through foggy conditions.
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