![]() ![]() If you focus on the wave crest that is just offshore of that little obstacle in the water (curious enough, a piece of brick wall), you clearly observe that angle. As you gain more point sources, the overall pattern becomes more even – to any one point, multiple point sources may create constructive or destructive interference – thus removing the clear distinction of specific minima and maxima)).A little more wave watching, today with a focus on how waves change direction when they run into shallow water. Let’s look at this beautiful wave and see what happens when it reaches the shallow shore.Ībove, you see the wake of the pilot ship, consisting of many wavelets that propagate as parallel wave crests towards the shore.īelow, you see that the wave is propagating at an angle to the shore (something around 45 degrees, maybe?). ![]() It doesn’t matter if the wave is light (as above, or sound or any other type) waves will diffract around barrier or through gaps of the appropriate dimensions (determined by comparing wavelength to gap width (why: as the gap is wider, more point sources can be accomodated. Here are two links ( 1, 2) that allow you to explore the effects of changing wavelength and gap size on the amount of diffraction occuring (and the number of maxima and minima produced). 1 λ/2, 3 λ/2, 5 λ/2 etc), then destructive interference will take place, creating a darker point (or minima). If the difference is odd number of half wavelengths (e.g. If this difference is whole number of wavelengths, constructive interference will occur, creating a bright point (or maxima). The distance from each point source to any point in the pattern is different, and if measured in wavelengths of the diffracted waves can be described as a difference in path length, or path difference. From our previous studies of superposition and wave mechanics, we know that if two waves interact, they may interfere constructively (creating a higher peak amplitude/ intensity) or destructively (creating a minimum height section). The wave passing through this gap acts like a sequence of point sources of light (to explain this, imagine each point source as a the source of a huyghen’s wavelet). This picture shows a straight wave approaching a gap that is four times as wide as the the wavelength of the wave (click to enlarge). The razor blade shadow above shows multiple diffraction shadow edges – but a better question might be why are there bright lines as well as shadows? This effect is strongest where the edge of the object is sharp and clearly defined. The region of gray-ness is where light is diffracting past an edge. These shadows aren’t simply black and white, the edge of each shadow grades from white to gray to black. You can see this when you turn on a single light (a point source, such as an LED, or stretching the definition slightly, a standard incandescent lightbulb), and look at the shadows produced. When light waves interact with a boundary, they too will bend. As you can see in the above picture, diffraction causes waves to to bend around an obstacle. ![]() Well, instead of looking for the waves themselves, we look for the effects of the diffraction. This behaviour is easy to see when the wavelength of the wave are so large as to be visible, but what about when they are so small that you cannot see the individual waves, like in light? ![]() You can see the straight waves approaching from the bottom of the picture and the waves becoming curved after they pass through the gap. In the picture to the left, ocean waves that encounter the gap between the peninsula and the islet are diffracted into the bay. Diffraction is a strange phenomenon that occurs any time light interacts with a opaque boundary. ![]()
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