Physics Demo Number: 053

Approximate Run Time: 5 min

Using a Water Stream as a Light Guide with the help of Total Internal Reflection

Demo Description

One exhibits total internal reflection of a laser beam inside a stream of water.

The stream is prepared for the laser beam insertion by the simple ploy of letting it flow out of a hole in the side of a Lucite reservoir.

Scientific Principles

• Total Internal Reflection (TIR)

Equipment

• Cylindrical Lucite water reservoir

• 5 mW Demonstration HeNe Laser

• Lab Jack for Matching Laser Height to Discharge Hole

• Mop Bucket

• Steel Cart

• Wood Platform Base

1

2

Equipment Location

• The bucket , reservoir, and Wood Base reside in Kit(053) on [C-1-5].

• The laser lives in [C-2-4]

• The Lab Jack lives in [G-1-6]

• Steel Cart is By Entry Door into Prep room from Hallway

                                                                                                                                                                                                                          3

Instructions

The first photo shows a cylindrical Lucite water reservoir with a smooth hole a few inches up from the bottom.

The hole is plugged with a removable red-rubber insert which may be removed to let water escape and form a streamlined laminar flow out of the hole into the galvanized bucket shown in the second photo.

If a laser beam has been aligned on the water side of the rubber plug, prior to removing the plug, then the laser beam will undergo multiple total internal reflections and stay inside the parabolic tube of water as it streams downward into the bucket.

However, the second photo shows that the tube of water breaks up fairly rapidly, so one needs the bucket up at the level of the steel cart as seen in the third photo.

If one fills the bucket with water to the level of the bottom ring seen on the inside of the bucket in the third photo, then pouring that amount of contents into the lucite cylinder gives a sufficient working level in the cylinder.

Writeup created by David A. Burba

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