Jello fiber optics

About two weeks ago we tried the jello fiber optics experiment but it hardly worked. A week ago, I found another recipe to make it, and this is what we used:

Purpose:  To investigate how fiber optics work by using gelatin and a laser pointer.



For a 5×9 inch loaf pan

  • 2 packages of light colored Jello gelatin (white grape is often recommended, but lemon is what we used)
  • 1 cup of hot water

For a 13×9 inch cake pan

  • 4 packages light colored Jello gelatin
  • 2 cups hot water
  • measuring cup
  • mixing bowl
  • laser pointer

Caution: hot water is a burn hazard.


Step 1. Mix hot water into jello until jello is thoroughly dissolved.

Step 2. Pour in pan and cool in refrigerator until solid.

Step 3: Cut into 1/2 – 1 inch strips.

Step 4: Dim lights and use the laser pointer at one end of the strip of jello at an angle and watch what happens. You might need to adjust the angle of the laser pointer. If you make a 1/2 inch strip or less, you can also make waves in the jello so that it’s not completely straight and see what happens.

And this is what you should get, more or less:


Why does this work?

Fiber optics work because of the way beams of light act when they strike the interface between two different materials. When light traveling through a medium such as water or glass hits the surface where the material meets the air, some of the light is reflected back inside the material and some may travel out into the air. The amount that is reflected depends on the angle at which the light hits the surface. If the beam hits the surface at a steep angle (that is, if the beam is nearly perpendicular to the surface), a lot of the light escapes into the air. On the other hand, if the beam hits at a very shallow angle, so that it just skims the surface, all the light is reflected back into the material; none is lost into the air. So when you shine a light in one end of a thin strand of glass, the light will stay entirely within the strand, glancing off its sides. Even if you gently bend the strand so that it curves a bit, the glancing beam of light will follow the curves all the way from one end of the strand to the other. (If you bend it too much, however, some of the light will strike the surface of the strand at too sharp an angle and will exit the strand, so that the light is not fully transmitted.)

(I forgot where I got this quote from, so if you recognize it, please let me know, I always attempt to cite the sources I get information from).

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