What happens to the velocity of light when it passes from a vacuum into air? My friend and I aren't sure what happens and we have a test on this. We both think it slows down.
2007-02-06 08:12:42 · 5 answers · asked by rawrxstephinator 1 in Science & Mathematics ➔ Physics
Both of you are correct.
It slows down. Light has a slower velocity in any medium containing "more" than a vacuum. It slows enough in water, for instance, for radiation emitted due to it to outpace it (this is called Cherenkov radiation).
Actually, it does not really ever slow. It moves at exactly its vacuum speed, but the material it is in essentially pushes back at it, some materials (water, say) more than others (air, say). So while its velocity never changes, its progress (and what we end up calling its speed in the particular material) does.
(Intriguingly (to me), something I have never seen addressed by writers of popular science is the fact that a vacuum is not devoid of matter and energy and one has to wonder if that means the vacuum has the same effect of pushing back? Implying that light's true velocity, were a true vacuum possible, would be even (though slightly) higher. If light would even exist under such a circumstance. It just doesn't seem to me such an easy question to definitively answer that it should be "intuitively obvious to the casual observer" and therefore not worth the time of said writers. I'd like one to address it sometime!)
2007-02-06 09:09:34 · answer #1 · answered by roynburton 5 · 0⤊ 0⤋
Light is slowed down when it passes through a medium (such as air), but the change is very, very, very slight, and it depends on many factors, such as the frequency of the light.
HOWEVER, this is only observed because the light is defracting a bouncing around and not moving in a straight line. Picture a ball in a pinball machine which always moves at a set speed. If it starts at the top and falls straight down, it will get there more quickly than if it hits several bumpers on the way.
So, the REAL speed of light never changes, but occasionally, there is a tiny experimental difference between the real speed and its observed rate of progression (speed) through a medium.
2007-02-06 16:22:27 · answer #2 · answered by Argon 3 · 0⤊ 1⤋
Light is at its speediest when in a vacuum. Entering air will thus slow it down, as a function of the index of refraction of the medium.
2007-02-06 16:22:40 · answer #3 · answered by Vincent G 7 · 1⤊ 0⤋
It will speed up, as in air there are particles and it an only travel at 99.7% of the speed it can in a vacuum.
2007-02-06 16:18:01 · answer #4 · answered by ? 2 · 0⤊ 1⤋
It will slow down.
2007-02-06 16:20:53 · answer #5 · answered by Lab 7 · 0⤊ 0⤋