Physics 122 3/11/11 Prof. E. F. Redish 1 3/11/11 1 Physics 122 3/11/11 2 Physics 122 3/11/11 4 Physics 122Physics 122 3/11/11 Prof. E. F. Redish 2 3/11/11 5 Physics 122 3/11/11 6 Physics 122 3/11/11 7 Physics 122Physics 122 3/11/11 Prof. E. F. Redish 3 3/11/11 8 Physics 122 Ripple tank analogy Can two sources lead to both “bright spots” and “dark spots”? 3/11/11 9 Physics 122 3/11/11 10 Physics 122 Ripple tank analogyPhysics 122 3/11/11 Prof. E. F. Redish 4 3/11/11 11 Physics 122 3/11/11 12 Physics 122 3/11/11 13 Physics 122 The wavelet model implies that a plane wave will travel in a straight line.Physics 122 3/11/11 Prof. E. F. Redish 5 3/11/11 14 Physics 122 http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=16 3/11/11 15 Physics 122 The wavelet model implies that a plane wave will reflect off a mirror according to the rule: angle of incidence = angle of reflection. 1. leading (left) edge of incoming wave (red) hits and starts outgoing wavelet (blue circle) 2. by the time the trailing (right) edge of the incoming wave hits the wavelet has grown this much 3. the trailing edge hits starting a wavelet and defining a wave front i f 4. Since the red and blue triangles are similar, i = f 3/11/11 16 Physics 122Physics 122 3/11/11 Prof. E. F. Redish 6 3/11/11 17 Physics 122 i 1. leading (left) edge of incoming wave hits and starts outgoing wavelet (blue circle) 2. by the time the trailing (right) edge of the incoming wave hits the wavelet has grown this much (v t) 3. the trailing edge hits starting a wavelet and defining a blue wave front 4. Since v t < c t, the triangles are NOT similar, and i > r Speed here = c Speed here = v r ct 3/11/11 18 Physics 122 i r c t v t i r sinsinsin sinirricthvthvc===11The wavelet model implies that a plane wave will refract into a medium according to the Snell’s law and tells us that n = c/(speed of light in the medium). http://www.walter-fendt.de/ph11e/huygenspr.htm http://www.phy.ntnu.edu.tw/java/propagation/propagation.html 3/11/11 19 Physics
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