1. JELL-O OPTICS

2. 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!

3. REFRACTION

4. What do lenses do?
Diverging Lenses (Concave shaped)

5. What do lenses do?
Converging Lenses (Convex shaped)

6. How Does Your Eye Work?
Objects form an upside-down image on the retina.
Lens
Focal point
Retina
object
image
Focal point
EYE

7. How Does Your Eye Work?
We will make a simplification: The image is at the focal point.
Lens
Retina
EYE

8. How Do We Correct Vision Problems?
Scientists and engineers have found ways to solve these problems.
Corrective lenses.
Glasses
Contacts

9. What is Near-Sightedness?
The eye is too long and the lens focuses light in front of the retina.
Lens
Retina
EYE

10. A Diverging Lens Corrects Near-sightedness
Retina
Lens
EYE
Diverging Lens

11. What is Far-Sightedness?
The eye is too short and the lens focuses light behind the retina.
Lens
Retina
EYE

12. A Converging Lens Corrects Far-sightedness
Retina
EYE

13. ENGINEERS CLEAR OUR VIEW
Thanks to Engineering and Science, millions of people have improved vision.

14. 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 <
ranges from cheap to very expensive.

15. 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!