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# Can "speed of light in still water" read as... watch

1. Can "speed of light in still water" read as "the speed of light with respect to water" ?
Even if water is moving

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2. No...

"The speed of light in still water" means "The speed with which an electromagnetic wave travels in still water."

The 'still' is there because the speed of light changes if the water is moving.
3. Thats not what Einstein says ...
4. (Original post by xiyangliu)
Can "speed of light in still water" read as "the speed of light with respect to water" ?
Even if water is moving

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It's basically the speed of light in water. It means where c is speed of light and nw is refractive index of water.
5. (Original post by teachercol)
Thats not what Einstein says ...
The refractive index of moving water is different there would be no change in the speed of light in a vacuum so Einstein would be fine.
6. (Original post by Qwertish)
No...

"The speed of light in still water" means "The speed with which an electromagnetic wave travels in still water."

The 'still' is there because the speed of light changes if the water is moving.
That is weird. The mark scheme states specifically that this has to be considered as the speed relative to water which I don't understand 0.o

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7. (Original post by k9markiii)
It's basically the speed of light in water. It means where c is speed of light and nw is refractive index of water.
Thanks. Why do they word a question like this. So confusing 0.o

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8. (Original post by teachercol)
Thats not what Einstein says ...
What?... >_>
9. (Original post by xiyangliu)
That is weird. The mark scheme states specifically that this has to be considered as the speed relative to water which I don't understand 0.o
That is a weird and ambiguous way of phrasing it...
10. (Original post by teachercol)
Thats not what Einstein says ...
lol... I think he means if the water is moving like, if someone is shaking the glass around and you're getting ripples in it. The density (and therefore refractive index) is different at different points in the glass, so the speed of the light wouldn't be the same everywhere.

Whereas you would be right if by "moving water", we just meant a glass of water, stationary with respect to the glass, but travelling at a constant velocity in some direction.
11. (Original post by tazarooni89)
lol... I think he means if the water is moving like, if someone is shaking the glass around and you're getting ripples in it. The density (and therefore refractive index) is different at different points in the glass, so the speed of the light wouldn't be the same everywhere.

Whereas you would be right if by "moving water", we just meant a glass of water, stationary with respect to the glass, but travelling at a constant velocity in some direction.

(Original post by Qwertish)
That is a weird and ambiguous way of phrasing it...

(Original post by xiyangliu)
Thanks. Why do they word a question like this. So confusing 0.o

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The phrasing isn't greatbut as tazarooni89 says it's considered with respect to flat water because the refractive index would not be constant in moving water. When it says with respect to or in relation to it just means taking that factor into account. They did not want you to use the speed of light in air.
12. (Original post by k9markiii)
The phrasing isn't greatbut as tazarooni89 says it's considered with respect to flat water because the refractive index would not be constant in moving water. When it says with respect to or in relation to it just means taking that factor into account. They did not want you to use the speed of light in air.
Yea, but "with respect to" is a bad phrase to use, because it brings up ideas of Spec Rel, with are completely irrelevant :/
13. (Original post by Qwertish)
Yea, but "with respect to" is a bad phrase to use, because it brings up ideas of Spec Rel, with are completely irrelevant :/
I use with respect to a lot. It's so common to use for me now at uni that I abbreviate it in notes. In this case the semantics aren't great but it's correct.
14. (Original post by k9markiii)
I use with respect to a lot. It's so common to use for me now at uni that I abbreviate it in notes. In this case the semantics aren't great but it's correct.
Really? Oh, I might as well start to get used to it then haha

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Updated: January 4, 2013
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