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1.

In the double-slit experiment of the gure, the viewing screen is at distance D = 4.90 m, point P lies at distance y = 20.5 cm from the center of the pattern, the slit separation d is 5.48 pm, and the wavelength A is 615 nm. What is the ratio of the intensity Ip at point P to the intensity Icen at the center of the pattern? Incident wave Reection by thin layers. In the gure, light is incident perpendicularly on a thin layer of material 2 that lies between (thicker) materials 1 and 3. (The rays are tilted only for clarity.) The waves of rays r1 and r2 interfere, and here we consider the type of interference to be either maximum (max) or minimum (min). The table below provides the indexes of refraction n1, n2, and n3, the type of interference, and the thinlayer thickness L in nanometers. Give the wavelength that is in the visible range. n1 "2 n3 Type L A 1.51 1.69 1.37 max 291 Calculate the minimum number of lines needed in a grating that will resolve a doublet of 551.0 and 551.9 nm in the second-order spectrum