UNIT EIGHT: Waves  Chapter 24 Waves and Sound  Chapter 25 Light and Optics

Chapter Twenty-Five: Light and Optics  25.1 Properties of Light  25.2 Color and Vision  25.3 Optics

Chapter 25.3 Learning Goals  Explain how basic optical devices function.  Compare and contrast the interactions of light and matter.  Distinguish between concave and convex lenses.

Investigation 25B  Key Question: How does light behave when its path is changed? Reflection and Refraction

25.3 Basic optical devices Three useful optical devices are: 1. lenses 2. mirrors 3. prisms

25.3 Basic optical devices  A converging lens bends light so that the light rays come together in a point.  This is why a magnifying glass makes a hot spot of concentrated light.  A mirror reflects light and allows you to see yourself.

25.3 Basic optical devices  A mirror reflects light and allows you to see yourself.

25.3 Basic optical devices  A prism, usually a solid piece of glass with flat polished surfaces, can both bend and reflect light.  Telescopes, cameras, and laser scanners use prisms.

25.3 Ways that light is affected by matter  When light interacts with matter, it can:  pass through almost unchanged (be transparent)  pass through but is scattered (be translucent)  bounces off (be reflected)  transfers its energy (be absorbed)

25.3 Ways that light is affected by matter  All four interactions almost always happen together.  The green shirt absorbs some light, reflects some light, and is partly translucent. Can you tell which colors are reflected and which are absorbed?

25.3 Light rays  Reflection occurs when light bounces off a surface and when light bends while crossing through materials.

25.3 Refraction  When light rays travel from air to water, they refract.  This is why a straw in a glass of water looks broken or bent at the water’s surface.

25.3 Law of reflection  The law of reflection states that the angle of incidence is equal to the angle of reflection.

25.3 Reflection  Not all reflections form images.  Rays light that strikes a shiny surface (like a mirror) create specular reflection.  Light rays reflected at different angles from dull or unven surfaces cause difuse reflection.

25.3 Refraction  Materials with a higher index of refraction bend light by a large angle.  The index of refraction for air is about  Water has an index of refraction of 1.33.

25.3 Refraction  Vegetable oil and glass have almost the same index of refraction.  If you put a glass rod into a glass cup containing vegetable oil, the rod disappears because light is NOT refracted!

25.3 Lenses  An ordinary lens is a polished, transparent disc, usually made of glass.  The shape of a converging lens is described as being “convex” because the surfaces curve outward.

25.3 Lenses  The distance from the center of the lens to the focal point is the focal length.  Light can go through a lens in either direction so there are always two focal points, one on either side of the lens.

25.3 Lenses  For a converging lens, the first surface (air to glass) bends light rays toward the normal.  At the second surface (glass to air), the rays bend away from the normal line.

25.3 Lenses  A diverging lens has concave surfaces.  For a diverging lens, you can show the focal point in a diagram by extending the path of the exiting light rays back through the lens.

Bioluminescence- Glow Live!  Like a glow stick, living things produce their own light using a chemical reaction. Bioluminescence is “cold light” because it doesn’t produce a lot of heat. While it takes a lot of energy for a living thing to produce light, almost 100 percent of the energy becomes visible light.