JELL-O OPTICS

How Does Light Bend?

• Refraction• Light travels slower through dense materials:

• Water

• Plastic / Glass &

• JELL-O!

• Light bends when it enters a substance at an angle.

• This is known as REFRACTION!

REFRACTION

What do lenses do?

Diverging Lenses (Concave shaped)

Converging Lenses (Convex shaped)

What do lenses do?

How Does Your Eye Work?

• Objects form an upside-down image on the retina.

Retina

Lens

EYE

objectimage

Focal point

Focal point

How Does Your Eye Work?

• We will make a simplification: The image is at the focal point.

Retina

Lens

EYE

How Do We Correct Vision Problems?

• Scientists and engineers have found ways to solve these problems.

• Corrective lenses.– Glasses

– Contacts

What is Near-Sightedness?

• The eye is too long and the lens focuses light in front of the retina.

Retina

Lens

EYE

A Diverging Lens Corrects Near-sightedness

Retina

Lens

EYE

Diverging Lens

What is Far-Sightedness?

• The eye is too short and the lens focuses light behind the retina.

Retina

Lens

EYE

A Converging Lens Corrects Far-sightedness

Retina

Lens

EYE

Converging Lens

ENGINEERS CLEAR OUR VIEW

• Thanks to Engineering and Science, millions of people have improved vision.

Materials List

• Two Laser Pointers (or other light sources)• Target Superstore for about $12.00 a piece.

• Knox gelatin

• 32 Envelopes for $10.00.

• Double the amount of gelatin in the recipe, this makes it very firm. Don’t add sugar or coloring.

• Put wax-paper into the pan before filling with gelatin so you can remove the gelatin in one piece.

• Converging and Diverging Lenses (optional)

• Edmund Scientific <www.scientificsonline.com>

• ranges from cheap to very expensive.

Demonstration

• Prepare gelatin the night before to allow it to set up.– Put wax paper into the gelatin pan so you can remove the gelatin out of the pan in one piece.

• Refraction demonstration. – Cut the gelatin with a sharp knife so you can shine lasers into a smooth flat surface. Do not use a serrated knife to cut the

gelatin, the surfaces must be as smooth as possible to minimize reflections at the surface.

– Shine a laser into the gelatin at an angle (like the sun picture).

– Move the laser (or gelatin) around to see different refraction angles.

• Lens demonstration.

– Shine parallel lasers through a diverging lens into the gelatin to see the divergence.

– Shine parallel lasers through a converging lens into the gelatin to see the convergence to a focal point.

– If you don’t have any lenses, cut lens shapes out of the gelatin for this part. It still works pretty well.

• Eye demonstration.

– Follow the figures and place a converging lens so that the laser focus on a “retina.” Move the lens closer and further from

the “retina” to simulate farsightedness and nearsightedness.

– Correct the vision with the appropriate lens.

• Conclusion.– Cut odd shapes out of the gelatin and let the kids shine lasers into them. Be creative!