Fun with lasers and gelatin

Physics of the Mundane

Adam Johnston

In this investigation, you will be studying some of the basic properties of light and how light can be manipulated.  You will utilize a laser, which provides an easily directed, straight beam of light.  Take heed: While the lasers we use are of relatively low power, they do provide a very concentrated amount of light, similar to those that are used for eye surgery.  Do not look directly into the source of the laser beam; and do not direct the beam towards others= lines of sight.

You may also use other light sources, such as small white flashlights or light sources that have multiple beams of light.  These may be especially useful in understanding how light is manipulated with lenses (see below).

We will also be using chilled gelatin for this lab.  Gelatin is mostly harmless and can be aimed directly at the eye if necessary.  It is also edible, although not necessarily appetizing.  You will be given a piece of gelatin, from which you may carve any necessary shapes.

During this laboratory, you should address the following issues:

C  Usually you can find the spot at which the laser is aimed, but you can=t see the beam itself.  When can you see the laser beam?  What must be done in order to see it?

C  One behavior of light is reflection, or the Abouncing@ of light off of some interface.  Using the gelatin, characterize reflection.  In what cases is a reflected beam brightest? In what cases is it most dim?

C  Another behavior of light is refraction, or the Abending@ of light as it goes from one medium (Astuff@) to another medium.  Characterize refraction.  In which cases does the light beam bend in, and in which cases does it bend out?  When is the refracted beam the brightest?  When is the refracted beam the most dim? 

C  You can cut lenses from your gelatin piece.  One kind of lens takes parallel beams of light and converges them to a point (known as a converging lens), and another kind of lens takes parallel beams of light and spreads them apart (known as a diverging lens).  Build these and describe them.

After lab, you should consider the following questions:

C  Refraction is caused because light travels at different speeds in different media.  That is, light is either speeding up or slowing down as it goes from one thing to another, causing it to bend. Explain where light is traveling the fastest and where it is traveling the slowest in this lab.

C  In answering the first lab question (above), you realize that in order to see the laser beam, there must be certain specialized conditions.  Describe the gelatin on the microscopic level, based on the fact that you can see the laser beam traveling through this medium.