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2. Reflection of Light When light is reflected off a surface the type of reflection depends on the smoothness of the surface. Regular reflection occurs when reflecting bodies are smooth such as a mirror, diffuse reflection occurs when the reflecting surface is light in colour but irregularly shaped and reflex reflection occurs when light is reflected from a manufactured surface such as traffic signs. Investigation #8 – Reflection in a Plane Mirror Normal line The following diagram represents how the lines and angles of incidence are related to the lines and angles of reflection. angle of incidence angle of reflection Reflecting surface Laws of Reflection 1. The angle of incidence is equal to the angle of reflection 2. The incident ray, the reflected ray and the normal to the reflecting surface lie in the same plane. If parallel beams of light fall on a polished surface, parallel beams are produced (regular diffusion). Obeying the law of reflection, that the angle of incidence = the angle of reflection, the parallel incident beams will produce parallel reflected beams. On the other hand if the beams of light fall on a rough surface (diffuse reflection) the rays have different angles of incidences and therefore travel in different directions. The diagrams below show both regular and diffuse reflection. a. Images in a Plane Mirror When you look into a mirror, you see an image of your face apparently located behind the mirror. If you move towards the mirror, your image will move closer to the mirror so that your image is always the same distance from the mirror as the object. If you raise your right hand the image on the mirror appears to be a left hand coming up to meet your right hand. Letters viewed in a plane mirror appear reversed horizontally but not vertically. This is called lateral inversion. The diagram below shows an example of lateral inversion. b. Applications of Plane Mirrors Plane mirrors have many applications one of which is a looking glass i.e. mirror. Other applications are: a) Cameras – Plane mirrors are used in the viewfinders of single lens reflex cameras (SLR’s). A mirror is hinged behind the lens of the camera. When the shutter is released, the mirror flips out of the way to let light fall on the film. As soon as the picture is taken the mirror flips back to the original position. b) Periscope – Used in submarines and created by using two plane mirrors facing each other. Assignment: Create a periscope using two plane mirrors and a piece of cardboard. c) Shooting Gallery – Bouncing light off of a mirror and hitting a target. d) Optical Lever – When a plane mirror turns through a certain angle and produces an image that turns through double the angle. e) Kaleidoscope – Two plane mirrors are arranged at 60° in a hollow tube. One end of the tube has an eyepiece and the other end coloured pieces of glass. As you turn the glass a variety of patterns are created. f) See-through Mirrors – Most mirrors made from glass have a reflective layer of silver. This layer is protected with an opaque coating. In see-through mirrors this coating is transparent. g) Theatrical Effects – Produces an illusion of a ghost. h) Right Angle Images – Produce three images. Turn in Assignment #3