![]() A horizontal vibrating beam is used to create plane waves.The legs of the ripple tank are adjusted so that the base of the tank is horizontal.The ripple tank is arranged as shown in Figure. ![]() Diffraction of Plane Waves in a Ripple Tank ExperimentĪim: To study the characteristics of diffraction of plane waves in a ripple tank.Īpparatus: Ripple tank with its accessories, stroboscope For smaller gaps and obstacles, the change of direction is more – the spread is bigger.Īmplitude: The amplitude of the diffracted waves is smaller than that of the incident waves. Speed: The speed of the diffracted waves is the same as that of the incident waves.ĭirection: The direction of propagation of the diffracted waves depends on the width of the gaps or obstacles. Wavelength: The wavelength of the diffracted waves is the same as that of the incident waves.įrequency: The frequency of the diffracted waves is the same as that of the incident waves. Diffraction of waves is a phenomenon that refers to the spreading out of waves when they move through a gap or round an obstacle.This observation can be explained by the diffraction of waves. It is noticed that when the waves passed through the narrow opening between the two concrete barriers, their shape changed. Figure shows a scenery of a fishing village.If D is greater than the wavelength there is at least one angle where destructive interference occurs the diffraction patterns in such cases are similar to the interference patterns produces by two sources close together. If D, the width of the opening, is less than the wavelength than there is no place where the interference is completely destructive. It turns out that the points where this destructive interference occurs are all along one line, at an angle (measured from a line perpendicular to the opening) given by: Similarly, the wave from the part of the opening next to the side will interfer destructively with the part of the opening next to the center, and so on - the waves from one half of the opening completely cancel the waves from the other half. This is the condition for destructive interference: the wave from the side of the opening will interfere destructively with the wave from the center of the opening. The waves from each piece of the opening are sent out in phase with each other at some places they will interfere constructively, and at others they will interfere destructively.Ĭonsider a point that is half a wavelength further from the center of the opening than from one side of the opening. If the opening is divided into many small pieces, each piece can be thought of as an emitter of the wave. Interference, both constructive and destructive, is important to understanding why diffraction occurs. The most interesting cases (i.e., the ones with interesting patterns of maxima and minima) are those in which the size of the openings or obstacles is about the same as the wavelength of the wave. When the sources send out waves in phase, constructive interference will occur at a particular point if the path lengths from the two sources to that point differ by an integral number of wavelengths.ĭestructive interference occurs at a particular point if the path lengths from the two sources to that point differ by an integral number of wavelengths + 1/2 a wavelength.ĭiffraction is the bending of waves that takes place when the wave encounters openings or obstacles. For a particular separation and wavelength, the pattern is as shown in the diagram, with constructive interference taking place at certain angles and destructive interference taking place at other angles. The sources are in phase with each other. Consider first the special case of two sources separated by a small distance d, sending out waves of the same frequency. When two (or more) waves of the same frequency interfere, a variety of different results can be obtained. The interference of two waves of the same frequency
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