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Ignore any parts of the wavelet outside of AOB. Side DI is shared for both triangles, sides IHG and INM must be equal if the rays are still parallel, and sides DG and DM must be equal assuming the speed of the wave is constant.
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Side DI is shared for both triangles, sides IHG and INM must be equal if the rays are still parallel, and sides DG and DM must be equal assuming the speed of the wave is constant. Since the two triangles are the same, all of the angles must be the same. Adjacent Angles Therefore, angle ADX must be equal to angle MDI and hence..
Since MNI is perpendicular to the rays, and the rays rotate by an angle a (where, [a+b] = 90o – qt), that means MNI also rotates by an angle a. Therefore … Similarly, a rotation of 90o by line DP makes … Using basic Trig it can be shown that … Using the expressions above and the following relationships and we can show that … b b b a a
This analysis can similarly be applied to and . Comparison of the three paths it becomes obvious that path is the shortest path, and therefore takes the least time. It should also be obvious that path requires that qi = qr.
Using the idea that light slows down in different media, but travels at a constant speed within each medium, we can determine the time it takes to go from A to B. Minimize the function:
Image Formation: Reflection Plane Mirror: This is the simplest type of image formation we can discuss for reflection. Object Location Image Location The path length (distance light travels along path) from the object to the observer must be the same as from the image to the observer. d d o i How far behind the mirror would the image be? qi qi Same distance that the object is in front of the mirror. qr Since the incident and reflected angles must be the same, and the total path length for the object and the image must be the same we can conclude that all distances relating the object to the observer and the image to the observer must be the same. Mirror Observer The image in the mirror is reversed front to back. The image formed for a plane mirror is called a virtual image. Virtual image – The light rays never pass through the image. Real image – The light rays do pass through the image