Understanding the Concept of Phase Velocity: Explained Simply

[KFC]

Hi all,
I have a difficulty to understand the concept of phase velocity of a wave packet. I read some materials online and my text, I didn't find a very straightforward explanation on this concept except the math definition. I also read some threads from this forum, but still have some questions.

From wiki, and I rephrase it as "the phase velocity is how the phase of any frequency component of a wavepacket moves". To me, it implies that all frequency components, if you staring at one particular point of each frequency component, they will move at the same pace? This is confusing because in one optical experiment on dispersion, we know that different color of light moves at different speed inside the prism. So is the traveling speed anything to do with this phase speed? If so, why here they said the phase speed same for all components.

I know that the light travel speed for different color is not same as the group speed since group speed means how fast the envelope travels.

 

[DuckAmuck]

Hi all,
I have a difficulty to understand the concept of phase velocity of a wave packet. I read some materials online and my text, I didn't find a very straightforward explanation on this concept except the math definition. I also read some threads from this forum, but still have some questions.

From wiki, and I rephrase it as "the phase velocity is how the phase of any frequency component of a wavepacket moves". To me, it implies that all frequency components, if you staring at one particular point of each frequency component, they will move at the same pace? This is confusing because in one optical experiment on dispersion, we know that different color of light moves at different speed inside the prism. So is the traveling speed anything to do with this phase speed? If so, why here they said the phase speed same for all components.

I know that the light travel speed for different color is not same as the group speed since group speed means how fast the envelope travels.

It's the same for all components in a vacuum.

 

[KFC]

It's the same for all components in a vacuum.

Oh, so to briefly summarize it, can I say phase speed is the speed of each frequency component composing the wave. Phase speed could be same or different for each component. If phase speed is different for each components, there will be dispersion.

 

[DuckAmuck]

Oh, so to briefly summarize it, can I say phase speed is the speed of each frequency component composing the wave. Phase speed could be same or different for each component. If phase speed is different for each components, there will be dispersion.

Seems correct to me. I think these pages will be helpful:
https://en.wikipedia.org/wiki/Phase_velocity
https://en.wikipedia.org/wiki/Group_velocity

 

[KFC]

thanks