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The phase velocity is the rate at which the phase of the wave propagates in space. The group velocity is the rate at which the wave envelope, i.e. the changes in amplitude, propagates. The wave envelope is the profile of the wave amplitudes; all transverse displacements are bound by the envelope profile.
Standard deviation diagram. The results of many tests using Zener cards fit with a typical normal distribution. Probability predicts these test results for a test of 25 questions with five possible answers if chance is operating: 79.3% of people will get between 3 and 7 correct. 10.9% will get 8 or more correct.
For example, a wavenumber in inverse centimeters can be converted to a frequency expressed in the unit gigahertz by multiplying by 29.979 2458 cm/ns (the speed of light, in centimeters per nanosecond); [5] conversely, an electromagnetic wave at 29.9792458 GHz has a wavelength of 1 cm in free space. In theoretical physics, a wave number, defined ...
The function s(x, t) is often called the source function because in practice it describes the effects of the sources of waves on the medium carrying them. Physical examples of source functions include the force driving a wave on a string, or the charge or current density in the Lorenz gauge of electromagnetism.
As waves cross boundaries between different media, their speeds change but their frequencies remain constant. Electromagnetic waves in free space must be solutions of Maxwell's electromagnetic wave equation. Two main classes of solutions are known, namely plane waves and spherical waves.
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For example, if an electron wave packet is initially localized in a region of atomic dimensions (i.e., 10 −10 m) then the width of the packet doubles in about 10 −16 s. Clearly, particle wave packets spread out very rapidly indeed (in free space): [17] For instance, after 1 ms, the width will have grown to about a kilometer.
A wavenumber–frequency diagram is a plot displaying the relationship between the wavenumber (spatial frequency) and the frequency (temporal frequency) of certain phenomena. Usually frequencies are placed on the vertical axis, while wavenumbers are placed on the horizontal axis.