Jan. 4, 2006

Water Optic Cable

Build a model of a fiber optic cable and discover more about reflection, fiber optics, and chemistry.

Description:

Internal reflection is created in a small water stream, replicating polymers that function similarly.

You Will Need:

1. empty, shiny, metal can
2. awl or hammer and nail
3. flashlight
4. tape
5. white paper
6. shallow pan or sink

Instructions:

This activity can be a bit messy.

Use a nail or awl to punch a 2-millimeter-diameter hole in the side wall near the bottom of an empty can. Use a piece of tape to temporarily seal the hole. Fill the can with water.

Place the water-filled can on a stand or another can. Dim room lights and direct a flashlight beam into the top of the water-filled can.

Remove the tape over the small hole, allowing water to flow in an arc out of the can into a basin. A spot of light should be visible at the splash point of the water stream. To facilitate observation of the light spot, you may need to position a piece of white paper at the splash point.

Content:

In this experiment, the stream of water is like the extremely pure glass used in the manufacture of fiber optic cable, which allows light to pass through undisturbed for long distances. The boundary surface between the water surface and air acts as a mirror because water has a higher index of refraction, or tendency to bend the path of light. If light should strike the side walls of the stream above a certain threshold angle, called the critical angle, it passes through the side walls. Below the critical angle, it is reflected as if it were bouncing off a mirrored surface.

In some applications, optic cables are preferred over common wires for sending information. Light impulses can carry more information and are not susceptible to interference as are electric impulses carried via metal wire.

Teacher's Notes

Activity excerpted by permission of the Chemical Educational Foundation (www.chemed.org) from You Be The Chemist. For additional information about these activities and lesson plans, see www.chemed.org/Kit.html.

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