![]() An example of diffraction phenomena is given by the spreading of waves around an obstacle. However, these behaviours also apply to other waves including sound waves and the other waves in the electromagnetic spectrum, the effects may just not be as great. Diffraction occurs if a wave encounters an object and if the wavelength is of the same size (or greater than) the object size. In this case on the left side of the source the waves will be out of phase and we see a wide ‘valley’ where the amplitude of oscillation is reduced. Light waves are often referred to when discussing reflection, refraction and diffraction. Now suppose that the distance between the source and the wall is equal to an odd number of quarter wavelengths (an integer number of half wavelengths plus a quarter of a wavelength). This animation shows the corresponding pattern: If the distance between the source and the wall is equal to a whole number of half wavelengths, then on the left side of the source the circular wave will interfere in phase with the reflection from the wall increasing the wave crest. Because of the wall, a reflected wave appears and interferes with the incident wave. Without the wall, the sound waves would travel outwards away from the source indefinitely. Light and sound waves do all kinds of cool stuff, because they can be in the same place at the same time, unlike matter. We now consider a three dimensional acoustic source located next to a rigid wall. The reflected wave pulse then travels from right to left, with the same speed and amplitude as the incident wave, but this time with the same polarity (the positive pressure pulse is reflected as a postive pulse). In order for the particle velocity to be zero at the wall the pressure gradient must be zero. Reflection of a sound wave at a hard wallĪt the wall there can be no particle motion, but the pressure can, and will, vary. Light waves are often referred to when discussing reflection, refraction and diffraction. A reflected wave pulse then propagates from right to left, with the same speed and amplitude as the incident wave, but with opposite polarity (the positive displacement of the string is reflected as a negative displacement). Diffraction, on the other hand, involves the spreading out of sound waves when they encounter obstacles or openings. ![]() Reflection of a transverse wave in a string which is at a fixed endĪt the fixed end, the displacement of the string remains zero and the reflected wave is a negative displacement. Refraction involves the bending of sound waves as they pass from one medium to another, while reflection involves the bouncing back of sound waves from a surface. The animations show the reflected wave (the black line) as well as its components (the red and blue lines). As a result, changing the medium (or its qualities) changes the speed of the wave. Refraction, or bending of the wave path, is followed by a change in wave speed and wavelength. The following animations illustrate how a wave is reflected when travelling until it reaches either a fixed or a free point. The bending of the sound waves when they enter a medium where the speed is different.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |