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Standing waves

When the reflection of waves occurs phenomenon overlay fluctuations. In figure. 24.20, as you can see, as the reflected waves are superimposed on the fundamental wave. This means, that each point on the surface of the water there, where the waves overlap, commits complex oscillation.

1

If by the end of the thread, thrown through block D (rice. 24.22), hang a small element out of the, and the other end of the thread bound to call molotočku, the fluctuations of the hammer on the threads run wave, that after reflection in point (D) is returned to the call. As a result of imposition of reflected waves on main thread retrieves the standing waves, named so because, that there is no displacement phase. While threads are clearly visible point, which do not fluctuate. These points are called nodes (A, In, (C) and (D)). Watching the variations threads, you can see, that all points between the nearest nodes are in the same phases, but have different amplitude. Such a point on threads, amplitude of which maximum, call pučnostâmi. For example, point (e) PIC. 24.22 is pučnost′û.

2

Continuing to monitor thread, you can see, and all the pučnosti nodes are in the same places threads. The distance between neighboring nodes is half the length of the standing wave. It turns out, that phase of the neighbouring poluvoln threads always points opposite. If at any time a thread takes the position, represented by a solid line, After half of the period it takes the position of, shown with a dashed line.

In the standing wave no such energy transfer, as in traveling wave: the sum of the energies of all points, located at a distance of a quarter wavelength, remains constant, While between these points and exchange of energy occurs. The reason is, что прямые и отраженные волны переносят энергию в противоположные стороны. Note, that standing waves occur only then, When the distance from the source of the waves to the obstacle, reflecting wave, fit integer quarters waves.

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