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Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
M Harish Kumar posted an Question
February 08, 2021 • 21:04 pm
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30 points
30 points
- CSIR NET
- Physical Sciences
What is the difference between group velocity and phase velocity
what is the difference between group velocity and phase velocity
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1. The phase velocity (wave velocity) of a wave is the velocity with which any given phase of the wave travels. It is given by vp=ωk. In a wave packet, the carrier wave travels with the phase velocity. But, when we deal with a particle or wave packet, the phase velocity isn’t important. Then the idea of group velocity comes into play. 2. In order to understand the nature of the group velocity, let’s consider a race. At any given instant, the velocity of a particular runner is different relative to others. Simply, the velocity of each individual runner within the group is different. But, they run within a group. The velocity at which the group of runners is moving can be considered as the group velocity in this simple example. It is given by: vg= dw/dk= vp+k dvp/dk see the attached figure for clarification. 3. The relationship between the phase velocity and the group velocity depends on the material properties of the medium. In non- dispersive mediums, the phase velocity of waves does not depend on the wavelength. So, the phase velocity equals to the group velocity. For example, the phase velocity is equal to the group velocity when sound waves travel through the air as air is a non- dispersive medium for sound waves.