Worlds Best Optical Illusion http://www.youtube.com/watch?v=haxm0diuyug Owls http://www.youtube.com/watch?v=hoc42xegvt8 Ray Diagrams http://www.youtube.com/watch?v=ed4jexpdwuo&feature=related 1
Locate Image formed by Plane Mirror using Ray Diagrams Perception and Rectilinear Propagation A ray of light travels in a straight line. The proper term for this is. From the moment we are born, when we reach out to touch things, our brain develops an understanding that light travels in a straight line. The complete process is as follows: light from a luminous object spreads out and fills the room light hits an object and the light interacts with the object some of the frequencies (colours) of light are absorbed and some are reflected. the rays of reflected light travel off in all directions some of which reach our eyes Our brain interprets this information by assuming the light traveled straight tracing the different rays back from both eyes to the place that these rays meet. person eyes object at a closer distance object Our brain determines the distance that an object is away by the angle differences of the rays which reach each of our eyes. This is called stereoscopic vision. Try this: Ask your neighbour to hold up their pen in a vertical plane (straight up and down), you cover one eye with your hand and try to touch the tip of the pen by bringing you finger down from above. Make sure you are over an arms length away. With one eye, you have no depth perception. Any idea of depth comes from your brains interpretation of size. When light hits a mirror, our brain still assumes that light travels in a straight line and so we take the rays back to the place where they meet object image 2
object image The image is really not behind the mirror no light travels behind the mirror. Instead, the mirror fools our mind because our understanding is that light travels in straight lines. Our brain traces the rays back straight back to the place where they would meet. Because no light really originated from this point, the image is said to be Due to simple geometry, the location of the image can be found by drawing a perpendicular line from the object to the mirror. The image will be at an equal distance behind the mirror. To complete this ray diagram: 1. find the image's location by drawing a perpendicular line from the object, across the mirror. 2. trace the ray straight back to find where the image would be 3
Steps for Drawing Plane Mirror Ray A ray that strikes the mirror at any angle reflects so the angle of incidence equals the angle of reflecon (The Law of Reflecon). The reflected ray is extended beyond the mirror. Incident 4
Examples: Locate the image for each of the following. Use a ruler and a sharp pencil 1. Finding the image 2. a) Find the image b) Trace 2 rays from the object to the eye (from 2 different points on the object). Notes: draw any ray behind the mirror with a dotted line to show that it is a virtual line. Add arrows to the rays to show which direction they travelled. 5
Locate the image for each of the following. Use a ruler and a sharp pencil Name: 1. Finding the image 2. Find the image and trace 2 rays from the object to one eye at 2 different points on the object. Draw any ray behind the mirror with a dotted line to show that it is a virtual line. Add arrows to the rays to show which direction they travelled. eye eye eye 6
Plane Mirrors What are common characteristics of your images? 7
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