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26_reflection_mirror - Lesson 26 Reflection Mirror Diagrams...

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Lesson 26: Reflection & Mirror Diagrams The Law of Reflection There is nothing really mysterious about reflection, but some people try to make it more difficult than it really is. All EMR will reflect off of appropriate surfaces, but for the purposes of this lesson we will only care about visible light reflecting off of mirrors. Drawings that show reflection always include a special line that must be drawn first... the normal . You might remember this word from when we studied forces. We say that a line drawn at 90° to the surface is a normal line . When you want to figure out how something will reflect from a surface, draw a normal line to that boundary at that point. The Law of Reflection says “ the angle of incidence equals the angle of reflection .” These angles are always measured from the normal line so that we have a common reference. In Illustration 1 we see that the angle is 42° coming in and 42° reflecting off. This is an example of regular ( specular ) reflection. The only time you need to be really careful with the law of reflection is when the surface is somehow irregular. We still draw normal lines, but we can end up with millions of them if the surface is really random. For example a lake on a windy day will show a really blurred image because the surface reflects the light in so many directions. We won't worry too much about this irregular (diffuse) reflection. Plane Mirror Diagrams We can use the Law of Reflection to draw diagrams to predict the way an observer will see an image in a plane mirror. “Plane” in this case refers to a boring, old fashioned, flat mirrors. Doing problems involving plane mirrors is actually pretty easy since we only have to remember a few things: 1. The image will be the same size as the original object. 2. The image will appear as far behind the mirror as the object is in front of the mirror. 3. The Law of Reflection . Any light beam that hits the mirror will bounce off at exactly the same angle. We assume the mirror is perfectly flat in these situations. We will have to make sure that the light rays reflected off the mirror do so at an angle that makes them hit the observer's eye. Let’s look at a simple example to illustrate how we have to draw these diagrams. 11/21/2010 © studyphysics.ca Page 1 of 10 / Section 13.3 Illustration 1: Reflection diagram.
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Example 1 : Sketch a ray diagram that shows how light will travel from the object to the eye by reflecting from the mirror in Illustration 2 . Identify the position of the image. First, measure how far the object is in front of the mirror. Draw a quick sketch ( Illustration 3 ) of the image behind the mirror at the same distance (just make sure it’s flipped around, and must be drawn with a dashed line).
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26_reflection_mirror - Lesson 26 Reflection Mirror Diagrams...

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