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Q:
how can light gain its original speed in vaccuum
after it passes through another medium e.g glass ?
- atimo (age 19)
univercity of khartoum, cairo, egypt
A:
That's a really nice question.
The odd thing is that even in a medium the basic electromagnetic
speed c is not really changed. However, all those charged particles
around are accelerated back and forth by the electromagnetic field, and
re-radiate their own fields. The reason that light travels slower
inside the medium involves a subtle cancellation between those fields
and the bare field of the initial incoming wave. Once the wave is back
out in the open, the only speed it can travel at, according to the wave
equation (from Maxwell's equations), is c.
I bet you can also see something like this with water waves travelling through regions with different depths.
Mike W.
(published on 10/22/2007)
Follow-up on this answer.
