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!
What do lenses do? Diverging Lenses (Concave shaped)
What do lenses do? Converging Lenses (Convex shaped)
How Does Your Eye Work? • Objects form an upside-down image on the retina. Lens Focal point Retina object image Focal point EYE
How Does Your Eye Work? • We will make a simplification: The image is at the focal point. Lens Retina 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. Lens Retina EYE
Diverging Lens Lens Retina EYE A Diverging Lens Corrects Near-sightedness
What is Far-Sightedness? • The eye is too short and the lens focuses light behind the retina. Lens Retina EYE
A Converging Lens Corrects Far-sightedness Converging Lens Lens Retina EYE
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!