![]() Looking at a straight object, such as a pencil in the figure here, which is placed at a slant, partially in the water, the object appears to bend at the water's surface. Refraction occurs when light goes through a water surface since water has a refractive index of 1.33 and air has a refractive index of about 1. Refraction in a water surface A pencil part immersed in water looks bent due to refraction: the light waves from X change direction and so seem to originate at Y. How much a wave is refracted is determined by the change in wave speed and the initial direction of wave propagation relative to the direction of change in speed.įor light, refraction follows Snell's law, which states that, for a given pair of media, the ratio of the sines of the angle of incidence θ 1. Refraction of light is the most commonly observed phenomenon, but other waves such as sound waves and water waves also experience refraction. The redirection can be caused by the wave's change in speed or by a change in the medium. In physics, refraction is the redirection of a wave as it passes from one medium to another. Why do we not see an infinite number of spots? What determines the maximum number of diffraction spots? Derive a mathematical expression for the maximum number of spots.Not to be confused with Diffraction, the change in direction of a wave around an obstacle.Ī ray of light being refracted in a plastic block Note that only 5 diffracted spots are visible with the 15,000 lpi grating.The grating material has aged over the past 10 years because of environmental effects. For the grating labeled 15,000 lines per inch, measure the diffraction angles of the spots, and use this information to compute the actual periodicity of the grating.Do the patterns from the gratings behave as predicted by the theory? Examine the Fraunhofer patterns from the three amplitude transmission diffraction gratings (labeled as 2,400, 7,500 and 15,000 lines/inch) and describe the patterns you see.What is the theoretically expected pattern as N → ∞. Sketch the pattern for various values of N and explain qualitatively what happens as N increases from 2.The number of slits, N, in each grating is indicated beneath each set of the gratings. ![]() ![]() These are contained on the bottom row of the plastic-mounted slide of 3.2. Set up and observe the Fraunhofer diffraction pattern due to the N-slit gratings. Provide a reconstruction of the slits, then compare their relative dimensions numerically. Using the captured image, employ Matlab to calculate the relative spacing of the slits. It is important that you not move the imager from its current location. Optional: Using the CCD imager, as shown in Figure 1, capture an image of the two-slit diffraction pattern.Explain why and how varying the slit separation affects the diffraction pattern.Rank the double slits in order of increasing separation. In addition, view the other double slits of varying separation on the top level of the same plastic slide.From your measurement calculate the slit width and the slit separation Sketch the pattern, and measure the angular distribution of the bright fringes for the double slit with the widest separation.These are contained on the upper level of the plastic slide labeled 3.2/3.3. Set up and observe the Fraunhofer diffraction pattern owing to the given double slits.
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