the speed of light

Light in a vacum travels at `c`.

When light passes through a denser medium it slows down.

Why does it speed up again when it passes back to a less dense medium?

For normal particles, friction in the more dense matter would slow it down and take energy from it, and that results it in not sppeding up again. Similarly friction would eventually stop it, but with light the speed is constant in any medium.

Is there more to it than simply `light will always travel at c if given a chance` relativity law?

Cheers,
~Al

Waves when travelling keep most of their energy.
What happens if waves in water pass through oil and then back into water again?
More or less same energy is retained but waves in the oil certainly look slower and smaller.
Perhaps this is because it takes more energy to move the oil but the energy is not dissipated.
Light being of dual nature must use it's natural waviness and curl to travel.

Thinking about it that way assumes that light must have an acceleration factor and that it would start at source with a speed of 0 and over some very small amount of time reach the speed of light.

IANAP (I am not a physicist) but I presume that at the quantum level the speed of a wave is consistent and compressed when passing through a medium therefore not slowing down only seeming to.

Interesting question though... I'm sure Brad would like his say

Waves when travelling keep most of their energy.
What happens if waves in water pass through oil and then back into water again?
More or less same energy is retained but waves in the oil certainly look slower and smaller.
Perhaps this is because it takes more energy to move the oil but the energy is not dissipated.
Light being of dual nature must use it's natural waviness and curl to travel.

At first I was a bit baffeled by Al's question but to me tihs explanation makes perfect sense!

Waves when travelling keep most of their energy.
What happens if waves in water pass through oil and then back into water again?
More or less same energy is retained but waves in the oil certainly look slower and smaller.
Perhaps this is because it takes more energy to move the oil but the energy is not dissipated.
Light being of dual nature must use it's natural waviness and curl to travel.

If 'light' has energy as it passes through the oil, it would have to use some of that energy to move the oil out of its way. Shouldn't this energy be dissipated? Thus slowing its speed down? Then when passing back to air, it continues at a slower speed, just still so fast we can't notice it?
Light cannot produce energy from nothing, because IT IS energy itself, and that same energy is constant under ideal conditions. The only factor that should either increase or decrease light's energy, is gravity. Thus, if we could measure the speed of light in oil, as we can in a vaccuum (186,282 or so miles per sec), then, would it change in space away from Earth's gravity?

Thinking about it that way assumes that light must have an acceleration factor and that it would start at source with a speed of 0 and over some very small amount of time reach the speed of light

Light should have an initial velocity speed, not an acceleration speed. How light is produced seems to show this. Light can be manipulated AFTER its 'inception', is this not right? Depending on the medium/media it travels through will influence its speed as it travels through space, both vaccuum and substance. We know gravity can change light by either bending and it or slowing it down or both at the same time. Lasers show how light is manipulated by a magnetic field (before the lens focusing it)...

This certainly gets the brain thinking!

Seanie.

I'm not the best when it come to physics, so please correct me if i'm wrong...

If the light travels through the denser medium it slows down.
Does this mean that while in the medium it's kinetic energy changes to potential energy?

Then after it travels back into the "normal" medium it's potential energy is released again allowing it to get back up to "c"?

Is this a fair assumption or have I just disgraced myself by forgetting all my Leaving Cert physics?

Michael