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Physics, Astronomy & Cosmology / Speed of light in different media
« on: 23/11/2005 12:28:48 »
The speed of light changes according to the media it is travelling through: the denser the material, the slower the speed.
Now, to my small brain, that doesn't hold water. The reason light appears to slow down is that when it travels through, say, a diamond, the photon is absorbed by a particle in the diamond which vibrates temporarily & then re-emits the photon. That doesn't mean the speed of light is slowed down, merely that its passage from 1 side of the medium to the other takes longer than it would take to travel the same distance in a vacuum.
Analogy. Imagine rolling a ball across a frictionless surface. Let's say it takes the ball 10s to roll 10m. That gives it a speed of 1m/s Now, imagine that there is a person standing halfway. Roll the ball to him. He holds it briefly before rolling it the remaining distance. The ball may well take more than 10s to travel the 10m, so its overall speed is <1m/s. However, whilst in flight the speed of the ball may well exceed 1m/s. The more people there are to catch & pass on the ball (equating to a denser medium), the slower its apparent speed when times from start to finish.
Therefore, it is the speed at which the photon travels between the particles in the medium which should be measured, not its average speed.
I thank yaw! []
Now, to my small brain, that doesn't hold water. The reason light appears to slow down is that when it travels through, say, a diamond, the photon is absorbed by a particle in the diamond which vibrates temporarily & then re-emits the photon. That doesn't mean the speed of light is slowed down, merely that its passage from 1 side of the medium to the other takes longer than it would take to travel the same distance in a vacuum.
Analogy. Imagine rolling a ball across a frictionless surface. Let's say it takes the ball 10s to roll 10m. That gives it a speed of 1m/s Now, imagine that there is a person standing halfway. Roll the ball to him. He holds it briefly before rolling it the remaining distance. The ball may well take more than 10s to travel the 10m, so its overall speed is <1m/s. However, whilst in flight the speed of the ball may well exceed 1m/s. The more people there are to catch & pass on the ball (equating to a denser medium), the slower its apparent speed when times from start to finish.
Therefore, it is the speed at which the photon travels between the particles in the medium which should be measured, not its average speed.
I thank yaw! []