7 ms·
This comes up from time to time with photons. It's usually the result of confusion over the difference between phase velocity and group velocity.
by kloch 3y ago
This comes up from time to time with photons. It's usually the result of confusion over the difference between phase velocity and group velocity.
- H8crilA 3y ago3blue1brown has recently released good YouTube videos on phase velocity. Question: how do I check group velocity in media, to know how fast information traverses through that media? For example in water - how long does it take for my waterproof flashlight to get across a small body of water? As in where to find that information. I always thought I just have to look up the index of refraction, but that's just the phase velocity.
- pfedak 3y agoThe index of refraction (including its dependence on frequency) fully describes the physics, there's nothing else to look up. Group velocity is a derived property taking into account the mathematics of waves, and in the typical textbook example of a very-nearly-monochromatic wave can be computed from the derivative of the index of refraction with respect to frequency.
- b112 3y agoWaait. OK. I get it. It's photons which make me look fat?
- verisimi 3y agoYep, sorry. You look the size of a football pitch, but your mass is only the size of a pea!