What is a wave? The one-dimensional wave equation
What is a wave? The one-dimensional wave equation
What is a wave? The one-dimensional wave equation
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2/3/14<strong>The</strong> Group VelocityTh<strong>is</strong> <strong>is</strong> the velocity at which the overall shape of the <strong>wave</strong>’s amplitudes,or the <strong>wave</strong> ‘envelope’, propagates. (= signal velocity)Here, phase velocity = group velocity (the medium <strong>is</strong> non-d<strong>is</strong>persive)D<strong>is</strong>persion: phase/group velocity depends on frequencyBlack dot moves at phase velocity. Red dot moves at group velocity.Th<strong>is</strong> <strong>is</strong> normal d<strong>is</strong>persion (refractive index decreases with increasing λ)4
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