Editing Tyndall Effect

{| class="wikitable" style="color:black; background-color:#ddd; margin-left: auto; float:right"
| [[Physics]]:
| Tyndall Effect, Micro-Particles
|-
| Grade Range:
| [[Elementary School]], [[Middle School]], [[High School]]
|-
| Format:
| [[Hands-on]]
|}

This demonstration is fun for students at hands-on events, especially since it can be seen from across the room. Have paper towels on hand in case students stick fingers in the water!


== Materials ==

* Glass Fish Tank
* Water
* Milk
* Large Spoon
* Red Laser Pointer
* Small Mirror
* Flashlight or Lamp

== Safety Precautions ==

Please read the General Safety Precautions section of the [[Demonstration Safety]] page before performing this demonstration.


== Demonstration ==

# Set the fish tank on a table and fill it 3/4 of the way with water. Slowly add milk to the water drop by drop while stirring, and use the laser pointer after each drop to make sure you get a dispersion that lets you see the laser. Set the mirror on the other side of the tank so the laser can be reflected back through.
# As students come up, let them come up and shine the laser through the solution. Ask them for ideas on why you can see the laser beam. What allows the laser to be visible?
# Have students to shine the lamp through the solution. They will see that the solution will appear blue, and the light bouncing off the mirror is red! What causes the separation of color?


== Why This Works ==

The ''Tyndall Effect'' is when light waves are scattered while traveling through a material or a liquid suspension. When we shine the laser through the solution, we can see the laser beam in the solution rather than just where it enters and exits. This is because some of the light is striking the particles in the solution and being reflected back towards us. Our milk/water suspension has tiny particles in it from the milk's proteins, sugars, and fat. These ''Micro-particles'' are extremely tiny, being 10,000 times smaller than a centimeter! Since these particles are extremely small, they have a big impact on what we see. This effect is substantial for light traveling through a liquid because the size of the solid particles that are suspended in the liquid can affect what wavelengths of light can pass through it.

White light from a lamp or flashlight contains light waves of all wavelengths. The waves of a shorter wavelength (blue, indigo, violet) are ''Scattered'' by the micro-particles from the milk. This means that these colors of light bounce off of the particles instead of continuing straight through the solution, and instead are reflected out of the fish tank. This is why the solution will appear to have a faint blue color from the light, instead of appearing to be a pure white! A thicker emulsion, or solution, will scatter more of the short wavelengths, creating a thicker apparent beam and a more defined color. The long wavelengths of light (red, orange, yellow) are less affected by the microparticles, and are able to travel all the way through the solution. This is why the beam that strikes the mirror appears red, even though we are using a white light!

== Additional Information ==

* Fog, a type of liquid aerosol colloid dispersion, also produces this effect. When headlights are turned on while driving through fog, the beam of light becomes visible due to the droplets suspended in the air.
* This demonstration can benefit from different types of suspended particles. Try it with things such as tiny sparkles, powders, and watercolor paints!
* This demonstration pairs well with other optics demos, such as the [[Light Box]] and the [[Box of Optics]] demonstrations.