The original poster inquires about the speed and momentum of a photon with a wavelength of 500 nm, expressing uncertainty about how to determine velocity without a mass.
The discussion has explored the nature of photon speed and the implications of medium on light propagation. Participants have provided clarifications and corrections regarding the constancy of c and the behavior of photons in various materials.
There is an ongoing examination of assumptions related to the question, particularly concerning the speed of light in different contexts and the original poster's understanding of the relationship between wavelength, speed, and momentum.
I laughed when I read this at first, but then I stopped laughing when I remembered that c varies. Quiz question -- why?chroot said:
berkeman said:I laughed when I read this at first, but then I stopped laughing when I remembered that c varies. Quiz question -- why?
And then there's the extreme case that came up in a thread recently with the apparatus that stops photons completely. That was weird.
Good point. I misspoke in an effort to be brief. c is indeed a constant, but the speed of photons depends on the medium. Thanks for catching my error.inha said:
Actually, I think even that's oversimplifying.berkeman said:Good point. I misspoke in an effort to be brief. c is indeed a constant, but the speed of photons depends on the medium. Thanks for catching my error.
Indeed, all photons travel at c; however, as has been said previsouly their rate of propagation can vary (depending on the medium). There is a related thread https://www.physicsforums.com/showthread.php?t=128221&highlight=photons+speed".DaveC426913 said: