Can the group velocity be greater than the phase velocity?

For most substances, therefore, the group velocity is smaller than the phase velocity. In such cases, it is mathematically possible that the group velocity may be larger than the phase velocity.

Is speed of light group velocity?

as well. To answer your question directly, what we usually mean by “speed of light” is the group velocity, as this is the one that Einstein’s postulate says should be constant (the max speed at which information can be transmitted).

Is the group velocity faster or slower than phase velocity?

But when a light pulse travels through a highly charged or dispersive medium, the two can differ. In normal dispersive media (such as in glass), the group velocity is slower than the phase velocity, and is the speed at which information can be transmitted. The NEC experiment shows faster-than-light group velocity.

Why can phase velocity be faster than light?

So if you interfere two plane waves propagating in opposite directions, but off by a fraction of a degree from being exactly opposite, the interference pattern will produce humps that propagate faster than the speed of light.

Is velocity of light the same as speed of light?

Light can travel in different directions. The speed of light is constant. The velocity of light should be, unless light changes direction. Speed is the magnitude of velocity, a scalar quantity (has size, but not direction), whereas velocity is a vector, which has both magnitude and direction.

Why group velocity is less than speed of light?

It is the group velocity which matters as that corresponds to the information speed. The motion of the wave group, not the motion of the individual waves that make up the group, corresponds to the speed of information. However, the waves themselves are not travelling faster than light.

How is velocity different than speed quizlet?

The difference between speed and velocity is that velocity has direction. Both of them involve distance and time, but only velocity involves direction. Acceleration is an increase or decrease in speed or a change in direction.

Can the phase velocity of a wave be greater than light?

It is my understanding the the phase velocity of a wave can be greater then the speed of light.

What is the difference between phase velocity and group velocity?

$\\begingroup$ The simple answer is that the wave packet travels at the group velocity not the phase velocity, and the group velocity is always less than or equal to $c$. You might argue that you aren’t using a wave packet.

Is relative velocity always less than the speed of light?

So actually, relative velocity always less then the speed of light. At the expense of no globally applicable definition. You can try to use a more globally applicable definition of cosmological velocities with that of a ‘proper distance’ but you then get galaxies that can move at greater then light speed.

What is the history of group velocity?

The idea of a group velocity distinct from a wave’s phase velocity was first proposed by W.R. Hamilton in 1839, and the first full treatment was by Rayleigh in his “Theory of Sound” in 1877. For light, the refractive index n, vacuum wavelength λ0, and wavelength in the medium λ, are related by