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Reflection and Light Flat Mirrors Reflection of Light • Reflection – the turning back of an electromagnetic wave at the surface of a substance – A good mirror can reflect about 90 percent of the incoming light • Diffuse reflection – light reflected from a rough textured surface – Reflected waves are scattered • Specular reflection – light reflected from a smooth shiny surface such as a mirror or still water – Light is reflected in only one direction Reflection of Light Reflection of Light • Incoming and reflected angles are equal – Law of reflection – the angle of incoming light ray is equal to the angle of reflected light ray in specular reflection • Angle of incidence – the angle between a ray that strikes a surface and the normal to that surface at the point of contact – Symbolized by θ • Angle of reflection – the angle formed by the line normal to a surface and the direction in which a reflected ray moves – Symbolized by θ’ Reflection of Light Flat Mirrors • Flat mirrors produce images behind the mirror – Virtual image – an image formed by light rays that only appear to intersect • Can never be displayed on a physical surface • Object distance – the distance from the object to the mirror • Image distance – the distance the image appears to be behind the mirror’s surface • Object distance and image distance are equal • Object size and image size are equal Flat Mirrors • Ray diagrams – drawings the use simple geometry to locate an image formed by a mirror • Draw the object and the mirror – Draw the image the same height and distance as the object • Object distance is called p • Image distance is called q Flat Mirrors • Draw two rays originating from the same location on the object – The first ray is perpendicular to the mirror’s surface • Since the reflected ray will be along the same path, make it a double headed ray – The second ray is not perpendicular • Draw the reflected ray; remember the angle of incidence equals the angle of reflection • Extend both reflected rays into the mirror (use dotted lines to represent rays into and behind the mirror) – Where they cross is the location of the image Flat Mirrors
