![]() Young's experiment with single photons.Introduction to Young's experiment, in which we explain Young's experiment and calculate the intensity as a function of angle.We can use the reflection conditions discussed here to predict the interference patterns that would be produced by reflection under different conditions and see whether that confirms or disproves the hypothesis. For two waves to be considered coherent, both waves need to have. But the ultimate test is of course experiment. What is coherent lightCoherence is defined as consistency, and that is exactly what coherent waves are. Reflections in strings and in optical media are mathematically analogous: Newton's laws for the string and Maxwell's equations for light. Indeed, light provides a window on the universe, from cosmological to atomic scales. On the grandest scale, light’s interactions with matter have helped shape the structure of the universe. ![]() The wave transmitted from glass to air has no phase change, and neither does the reflected wave. Light from the Sun warms the Earth, drives global weather patterns, and initiates the life-sustaining process of photosynthesis. (See Geometrical optics for futher discussion of reflection, refraction and phases.) ![]() The transmitted wave has no phase change, but the wave reflected in air has a phase change of π. Therefore the wavelength in glass is smaller. At the interface, the oscillation in the fields has the same frequency so both waves have the same frequency. Note that, in glass, the speed of light is slower ( n higher) than in air. (Although we don't show it here, we also get these predictions for the phases by imposing the boundary conditions on the electric field and displacment at the interface: the speed of light is slower in glass because its dielectric permettivity is higher.)īefore we test these predictions, let's look at the wave behaviour in the following animations. And, in both cases, the transmitted wave has a phase change of zero. Going from glass towards air, we expect reflection with a phase change of zero. So, going from air towards glass (low n towards high n), we expect light to be reflected with a phase change of π. It is made of little packets of energy known as photons. Glass is analogous to the heavy string in the clips above. Light is the only electromagnetic radiation that is visible to the human eye. (See Geometrical optics for an introduciton.) So the speed of light in glass (by definition c/ n) is slower than that in air. That for glass is somewhat higher: n ~ 1.5 here. The refractive index for air is very nearly 1. Part of the incident energy is reflected and part is refracted. Here a ray of light in air meets the interface with glass.
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