Phase velocity Definition and 82 Threads

When something has a phase velocity greater than the speed of light,will it travel backwards in time in one frame?

I know the phase vs group question has been asked before, but I really don't quite understand it. I've read in various places that the phase velocity of a light wave has been made to go faster than C, and in others that the group velocity has been made to go faster than C, and even made negative...

understanding for group velocity and phase velocity?? Hi, everyone. I learned physics for 3 years, but up to now I still cannot understand clearly the difference between the group & phase velocity. What is exatly "phase"? and what is exactly "group". From book I read the Vph corresponds to the...

Group and Phase velocity of Light I read that in cases of anomalous dispersion, the group velocity of an electromagnetic wave can exceed the speed of light c in a vacuum. How does this fit in relativistically?

In quantum mechanics, particles also behave as waves with complex phases. By the de Broglie hypothesis, we see that Vp=w/k=E/p Does have relation Volt with momentum or wavnumber(2Pi/wavelenght) ? and current with phase velocity ?

"Group velocity (equal to an electron's speed) should not be confused with phase velocity (equal to the product of the electron's frequency multiplied by its wavelength)." Above statement is from wikipedia, and I still don't quite understand it. As one of the postulate of QM, group velocity...

Homework Statement The phase velocity of each wavelength of white light moving through or- dinary glass is a function of the wavelength i.e. glass is a dispersive medium. What is the general dependence of phase velocity on wavelength in glass? Is dvp/dlamda positive or negative? Why...

What is actually phase velocity?? When a body moves aren't we supposed to say that each particles on the body moves with same velocity and so the de-broglie wave corresponding to each particle must have the same velocity. Then why should a wave representation of moving body correspond to a...

When someone asks the question why can some stuff go faster than c, they get the answer that "it's not a transfer of information- special relativity says that no INFORMATION can travel faster than light." Why don't processes such as phase velocity and entangelment transmit information? What...

Homework Statement Given: angular frequency=2000pi phase velocity=320m/s period=? unknown Homework Equations f=w/2pi; w=omega. T=1/f. phase velocity = lambda/T The Attempt at a Solution i don't know what the sgnificance of the phase velocity is. this is because from 1/T = w/2pi, i...

I know the definition of group and phase velocity but why? Why they are different and what's the physics behind it to define such velocities?

OK, I think I understand the problem, I'm just a little confused on some pieces in the middle. Problem: Consider a wave packet formed by the superposition of two waves psi1=cos(1.00x-2.00t) <--1.00=k, 2.00=w psi2=cos(1.01x-2.03t) <--1.01=k, 2.03=w where x...

With: wavelength = 4 meters frequency = 30 cycles/sec period, T, = .033 sec/cycle wave propagation velocity = 120 m/s wave number ,k, = 2pi/wavelength = 1.57 radians/meter angular frequency, w, = 2pi/T = 188.5 radians/sec phase velocity = w/k = 120m/s In the above propagation...

Homework Statement wavelength = 3m frequency =25 cycles/sec period T = 1/frequency = .04 sec/cycle wave propagation velocity =75 m/s wave number K = 2pi/wavelength= 2.09 radians/m angular frequency w = 2pi/T = 157 radians/s phase velocity Vp = w/k = 157/2.09 =...

At low velocity the group velocity is double the phase velocity (velocity of de Broglie waves). But phase velocity is more than the speed of light and group velocity is the velocity of particle. This means that particle velocity is also more than speed of light. But This seems to violate the...

Can an electromagnetic wave have a phase velocity greater than c? Is the phase velocity of a photon always c? As far as I understand, the phase velocity of all massive particles (particles with rest mass) is greater than c.

What are the limitations on the phase velocity of laser light? Is it true to say that the phase velocity of laser light is limited to <c?

Homework Statement If \Psi = f(x, y) and x = g(t), y = h(t), then (d\Psi / dt) = (p\Psi / px)(dx / dt) + (p\Psi / py)(dy / dt), where "p" symbolizes the partial derivative here and throughout the rest of this posting. Derive the phase velocity equation +/- v = -(p\Psi / pt) / (p\Psi / px)...

Homework Statement Consider electrons of kinetic energy 5eV and 500keV. For each electron, what would be the particle speed, phase velocity, group velocity, and Broglie wavelength? Homework Equations lambda = h/p (lambda = broglie wavelength) K.E. for nonrelativistic calcualtion =...

Homework Statement Given... v\left(z,\,t\right)\,=\,5\,e^{-\alpha\,z}\,sin\left(4\pi\,\times\,10^9\,t\,-\,20\pi\,z\right) where z is distance (m), find... (a) Frequency (b) Wavelength (c) Phase Velocity (d) At z = 2m, the amplitude is 1 [V], Find the attenuation constant (\alpha)...

Is there any unconventional method to find out the relation between group velocity and phase velocity? know there is a method employing Fourier tarnsforms and another easier method as well

ok so the picture I get in my head is: if I took a wave, and stretched it so that it was a straight line, the phase velocity would be the speed at which a point travels along that line. is that an accurate analogy or am I way off?

Homework Statement Consider the simplified wave function: \psi (x,t) = Ae^{i(\omega t - kx)} Assume that \omega and \nu are complex quantities and that k is real: \omega = \alpha + i\beta \nu = u + i\omega Show that the wave is damped in time. Use the fact that k^2 =...

I am really stucked with my homework problem.Can anybody help me. The dispersion relation for free relativistic electron waves is w(omega)=(c^2k^2+(m(mass of electron)c^2*2pi/h)^2)^0.5 Obtain expression for the phase velocity Vp and group velocity Vg of these waves and show that...

Obtain the group velocity v_g and phase velocity v_p of 7.0 MeV protons/electrons. Write each answer as a multiple of the speed of light c. My work: 1. Finding the group velocity: v_g = \frac{\partial \omega}{\partial k} = \frac{\partial \left( E / \hbar \right)}{\partial \left( p /...

In a plasma for instance, the dispersion relation is k^2=\omega ^2 \epsilon_0 \mu_0 -\epsilon_0\mu_0 \omega_p^2, where I have made the approximation that the permitivity and permeability in a plasma are about those in empty space. Let's take the case where k is real (which happens as soon as...

Hi do u know what phase velocity is>? I have found it a boot for optical fibers vp=1/(srqt(em) m denotes greek m letter

Would someone be kind enough to please give physical meanings to these two terms? I have never fully understood their meaning and difference (although I know how to express them mathematically). If, say, I have a Gaussian-shaped signal in the frequency domain that I am sending through a...

We are asked to substitute a plane wave solution into the TDSE for V=0 and show that it satisfies the TDSE (this is straightforward). Does this mean the plane waves are only solutions to the TDSE if V=0, or do they have other significance? Also we show that the group velocity = v (the...

why is phase velocity v=w/k ?

undefinedundefinedWhat are group velocity and phase velcity? What are it's physical implications? :smile:

I am kind of stuck in a question relating to phase velocity and group velocity. I have been given that the index of refraction of a media is inversely propotional to the vacuum wavelength. And we are supposed to show the group velocity is half the phase velocity. Now, the work I have done...