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

25.3 Four ways light is affected by matter  A glass window is mostly transparent, but also absorbs, scatters, and reflects some light.  See if you can identify where certain colors are absorbed and reflected in this picture.

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

25.3 Reflection  There are two types of reflection; but not all reflections form images.  Rays light that strikes a shiny surface (like a mirror) create single reflected rays.  This type of reflection is called specular reflection.

25.3 Reflection  A surface that is dull or uneven creates diffuse reflection.  When you look at a diffuse reflecting surface you see the surface itself.

25.3 Law of reflection  A ray diagram is an accurately drawn sketch showing how light rays interact with mirrors, lenses, and other optical devices.

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.