All Questions
7
questions
3
votes
2
answers
306
views
Speed of photon
Background:
I originally asked this question
Does a single photon propagate with phase velocity or front velocity through a dispersive material? about the speed of a single photon in a dispersive ...
- 1,803
4
votes
1
answer
650
views
Does phase velocity or group velocity change when light enters a new material? Contradictory sources
I'm so confused. I've read in this book (page 28) that group velocity of light can exceed $c$ in certain gases. However a lot of people online and in the forums say that phase velocity can exceed $c$.
...
- 143
8
votes
2
answers
1k
views
What really is the speed of light in a medium/vacuum, group or phase velocity?
While reading about refractive index 2 terms popped up, group velocity which alway slows down in a medium and phase velocity which may exceed speed of light. Say in a complete vacuum and using laser ...
- 13k
3
votes
1
answer
206
views
Why is refractive index equals to speed of light upon phase velocity and not group velocity?
We have been using group velocity for most purposes as its the velocity with which the wave packet travels, they why do we use phase velocity for calculating refractive index.
1
vote
1
answer
800
views
Why phase velocity of light is slower in a dielectric than vacuum?
Why does light speed suffer a reduction when it passes through a homogeneous dielectric medium? I know my math says so, i.e.- a highly polarizable ($\chi$) medium is associated with high $\epsilon$ (=$...
- 31
2
votes
3
answers
4k
views
Two different mediums can have equal index of refraction?
In other words: given a certain medium, is light's phase velocity unique?
- 133
5
votes
1
answer
612
views
Fermat principle: which index of refraction?
I am somewhat puzzled by a common formulation of the Fermat principle (light travel time), because it contains index of refraction related to phase velocity while light travel time through a slab of ...
- 2,163