Light through a mixture
Show on a big screenA thin beam of light enters a dark room. Suddenly you can see the dust floating in the beam. The dust scatters the light. That means the dust sends light off in many directions.
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- A torch shines into two liquids.
- Solution: the beam leaves no path.
- Colloid: a bright path shows.
The rule
Light scatters off the pieces in a colloid or a suspension. A true solution hardly scatters light. This scattering is the Tyndall effect.
Solution pieces are so small that they hardly scatter light. The pieces of a colloid are big enough to scatter it. Dust and smoke scatter light too. You see this in a floodlight beam.
Never look straight into a laser beam. It can hurt your eyes.
Naming the parts of a colloid
In a colloid, the spread-out pieces are the dispersed phase. What they are spread through is the dispersion medium. In milk, drops of fat are the dispersed phase. Water is the medium.
A colloid of one liquid in another liquid is an emulsion. Milk is an emulsion.
Try the lab to finish this lesson.