Untitled Document

Physics Demo Number: 130

Approximate

Run Time: 5 to 20 min

Snell's Law With The Aid of A Smoke Box and ATray of Soapy Water

Demo Description

Introduce a beam from a strong laser outside of a smoke box and watch it being refracted into a container of soapy water inside the box.

Scientific Principles

Reflected and refracted rays can be made visible by scattering from smoke particles and soapy water.
Snell's Law

Equipment

Smoke Box
Soapy Water Container
Box of Powdered Ivory Snow
5 mW Laser

Equipment Location

Smoke Box [C-3-2] and [C-3-3]
Soapy Water Container and Soap Kit (130) on [C-3-3]
Main Box of Soap in Kit (041) on [C-2-5]
Laser on [C-2-4]

Instructions

Laser light travels a straight, but invisible line through the air, becomes visible on entering the smoke box and is clearly refracted toward the normal as it enters the soapy water solution. Note that lenses are not needed for this demonstration and that if only this demonstration is being done, one could use just half of smoke box to simplify setup (see demo018).

The second photo shows the setup with more room lighting turned on

The third photo

indicates that there is a reflected component of the laser beam from the water surface as well as the refracted component.

The last photo shows rectangular tank from [C-4-3] with soapy water inside.

Spray mist can be used in the air in the tank to replace the smoke tank used for Snell's Law in the first picture.