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Al Tobias (wat4y) - Office: Gibson S123 & Physics 218, (434) 924-0538

Physics Demo Manual

Demonstrations are cataloged according to PIRA Bibliography

PLEASE REQUEST DEMOS WELL IN ADVANCE

Due to Physics Building renovations, the lead time to set up demo requests has increased due to the need to transport equipment across campus. Please be kind and let me know well ahead of time what you need.

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 Geometrical Optics
 Diffraction
 Interference
 Color
 Polarization
 The Eye
 The Eye Model I
 The Eye Model II
 Image Retention

The Eye Model I

Purpose:

Demonstrate the optics principles of operation of the human eye.

Procedure:

There are many eye conditions one can illustrate with the Denoyer-Geppert Eye Model #602. Details are explained in the manual.

Choose the distance from the cornea to the retina by sliding the strap/ruler on top of the model. Focus the "AE" image from the light box onto the retina and demonstrate that the image goes out of focus when the lens curvature is changed by adding/taking away water (effective near or far sight). Demonstrate that adding the appropriate corrective lens in front of the eye "cures" the near or farsightedness.

Farsightedness (Hyperopia) - objects far away look sharp & clear, but near objects do not come into focus. This is due to either the eye's lens (cornea) not being curved enough or the eyeball being too short, causing the image to focus beyond the retina. Typically one needs a convex (positive diopter or plus powered) lens for correction, which moves the image forward and correctly focuses properly on the retina. We have a +1.0 convex lens for this model. It's shaped like a dish, but is thick in the center and thin on the edge.

Nearsightedness (Myopia) - objects far away are unfocused & fuzzy, but near objects are sharp & focused. This is due to either the cornea being curved too much or the eyeball being too long, causing the image to focus short of the retina. Typically one needs a concave (negative diopter or minus powered) lens for correction, which moves the image back and focuses properly on the retina. We have a -0.5 concave lens for this model. It's shaped like a dish, but is thin in the center and thick on the edge.

Hints:

Make sure that syringes have enough water to fill the entire eye, otherwise the lens focal length might not be short enough to focus the image on the closely set up retina.