| A | B |
|---|
| light-year | the distance that light travels in one year |
| transverse wave | a wave shaped like a water wave |
| ray | a line that shows the direction of a light wave |
| luminous objects | objects that give off their own light |
| illuminated objects | objects that light shines on |
| point sources | a tiny point of light |
| extended source | a light source made up of many point sources |
| opaque materials | materials that block all light |
| transparent materials | materials that let light pass straight through them |
| translucent materials | materials that let some light pass through |
| umbra | a sharp, black shadow |
| penumbra | a gray, outer shadow around an umbra |
| reflected light | light that has bounced off something |
| incident ray | the ray of light that hits something |
| reflected ray | the ray of light that bounces off something |
| normal line | a line drawn at right angles to a surface |
| angle of incidencse | the angle between the incident ray and the normal line |
| angle of reflection | the angle between the reflected ray and the normal line |
| image | reflection in a mirror |
| regular reflection | reflection from a smooth surface; reflection that gives clear images |
| diffuse reflection | reflection from a rough surface; reflection that does not give images |
| media | more than one medium |
| refraction | the bending of light as it passes from one medium to another medium at an angle |
| lens | a curved piece of glass |
| convex lens | a lens that is curved outward |
| concave lens | a lens that is curved inward |
| focal point | the place where light rays from a lens meet |
| focal length | the distance from the focal point to the lens |
| real image | an image that can be projected |
| cornea | the clear front of the eye |
| pupil | the opening into the eye |
| iris | the part that controls the amount of light entering the eye |
| retina | the back part of the eye on which images form |
| optic nerve | the nerve that carries signals from the eye to the brain |
| visible spectrum | the seven colors of the rainbow |
| prism | a triangular-shaped piece of glass |
| ultraviolet light | invisible light with wavelengths shorter than violet |
| infrared light | invisible light with wavelengths longer than red |
| electromagnetic spectrum | the spectrum made up of radio waves, infrared, visible light, ultraviolet, X rays, gamma rays, and cosmic rays |
| absorb | soak up |
| transmit | allow to pass through |
| filter | a material that transmits some colors of light and blocks others |
| photoelectric cell | a cell that changes light into electricity |
| photon | a tiny particle of light |
| laser | a device that makes one-color, high-energy light |
| hologram | a 3-D photograph made with a laser |
