Ch. 2.3 REFLECTION AND REFRACTION Reflection Reflection occurs when an object or wave bounces back off a surface through which it cannot pass Law of reflection: the angle of incidence equals the angle of reflection Mirrors Plane mirrors – flat sheet of glass that has a smooth, silver-colored coating on one side. Image – copy of an object formed by reflected or refracted rays of light Virtual image – an upright image that forms where light seems to come from. Your image appears to be behind the mirror. Mirrors cont’d Concave mirrors - a mirror with a surface that curves inward like the inside of a bowl Optical axis – imaginary line that divides a mirror in half Focal point – the point at which rays parallel to the optical axis meet or converge Real image – forms when rays actually meet. Virtual images formed by a concave mirror are always larger than the object. Mirrors cont’d Convex Mirrors – a mirror with a surface that curves outward. Convex mirrors can NEVER create a real image Ex: security mirrors and safety mirrors in banks, parking garages. Allows you to see a larger area than you can with a plane mirror. Refraction Light travels in straight lines IF the medium it travels through does not change. If light enters the new medium perpendicular to the boundary, it will keep moving in the same direction If it hits the boundary at an angle, it will bend. – bending of light waves due to a change in speed is called the refraction. Refraction cont’d Refraction in different mediums When light rays enter a medium at an angle, the change in speed causes the rays to bend, or change direction. Diff. Densities within the same medium can cause refraction as well. EX. Air heated by a campfire can cause objects to appear shimmer. Stars twinkle due to variations in the atmosphere density. Refraction cont’d Effects of refraction – separation of visible light into its component colors by a prism. Difference in refractions causes white light to spread out into the colors of the spectrum : ROYGBIV Water droplets can cause the same effect – rainbow Pencil in a glass Lenses Lens is a curved piece of glass or other transparent material that refracts light. The type of image formed by a lens depends of the shape of the lens and the position of the object. Lenses cont’d Convex lenses – (magnifying glass) thicker in the center than at the edge. An object’s position relative to the focal point determines whether a convex lens forms a real image or a virtual image. (see fig 19, pg. 59) Lenses cont’d Concave lenses Concave lens is thinner in the center than at the edges. A concave lens can produce only virtual images because parallel light rays passing through the lens never meet.