lecture 22

# lecture 22 - 25.3 Plane Mirrors Look into a plane mirror...

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25.3 Plane Mirrors Look into a plane mirror. What are the properties of the image you see? 1. The image is upright. 2. The image is the same size as the object. 3. The image is located as far behind the mirror as the object is located in front of it. 4. The image is reversed from left to right. Let’s see how an image is formed with a plane mirror: First, I can use a ray that goes straight over and reflects straight back. Now use a second ray which comes up from the object at some angle. θ r θ i Extrapolate the second ray back behind the mirror. The two extrapolated rays intersect at the Object Mirror The two extrapolated rays intersect at the image. Image

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θ r θ i The image formed by a plane mirror is called a virtual image. Virtual, since the light rays only appear to come f th i b t th d t t ll t from the image, but they do not actually emanate from there. Question : I want to use a plane mirror to see Object Mirror Image my entire body. How long does the mirror have to be? A ray from the top of my head will strike the mirror and enter my eyes as shown. And, a ray from my foot can strike the mirror and enter my eyes as well. Wall Extrapolating these rays back will show the location of the image. Any other ray from above my foot, like Any other ray from above my foot, like from my waist, would have to strike the mirror above the point where the ray from my foot did. Th t ti b d I l d Thus, to see my entire body, I only need a mirror that is ½ my height. Note: It doesn’t matter how far I am from the mirror either!