Refraction and Lenses

1. Refraction and Lenses • Refraction = the change in direction when light enters a material with a different speed of light • Light slows down when in glass vs. air. • Light changes direction when it enters the glass and slows down. • It changes direction when it leaves the glass and speeds up again.

2. Why does it change direction? Waves move slower in a more dense medium than in a less dense medium and vice versa.

3. Concave vs. Convex

4. Lenses • Convex or converging lenses (like a magnifying glass) – direct light inward or focus light to a point • Concave or diverging lenses – direct light outward

5. Far vs. Nearsightedness • Farsightedness. Light rays entering the eye — particularly from nearby objects — will not be brought to a focus by the time they strike the retina. Far away objects can be seen more easily. Farsightedness is called hypermetropia. • Nearsightedness. The image of distant objects is brought to a focus in front of the retina and is out of focus again before the light strikes the retina. Nearby objects can be seen more easily. Nearsightedness is called myopia.

6. What it looks like… • Farsightedness – focuses behind retina – need a convex lens to correct • Nearsightedness – focuses in front of the retina – need a concave lens to correct

7. Other interesting light stuff… • Total internal reflection • Cool prism demos • Optical fiber demo and use • Total internal reflection and refraction • RAINBOWS • Double rainbows • Polarized Filters • Sunglasses • Window tint