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

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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Reply 1

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.

Reply 2

teachercol

Thats not what Einstein says ...

Reply 3

k9markiii

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

Posted from TSR Mobile

It's basically the speed of light in water. It means

\frac{c}{n_w}

where c is speed of light and n_w is refractive index of water.

Reply 4

k9markiii

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.

Reply 5

xiyangliu

Original post by Qwertish

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

Posted from TSR Mobile

(edited 11 years ago)

Reply 6

xiyangliu

Original post by k9markiii

It's basically the speed of light in water. It means

\frac{c}{n_w}

where c is speed of light and n_w is refractive index of water.

Thanks. Why do they word a question like this. So confusing 0.o

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Reply 7

Qwertish

Original post by teachercol

Thats not what Einstein says ...

What?... >_>

Reply 8

Qwertish

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... :confused:

Reply 9

tazarooni89

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.

Reply 10

k9markiii

Original post by tazarooni89

Original post by Qwertish

That is a weird and ambiguous way of phrasing it... :confused:

Original post by xiyangliu

Thanks. Why do they word a question like this. So confusing 0.o

Posted from TSR Mobile

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.

Reply 11

Qwertish

Original post by k9markiii

Yea, but "with respect to" is a bad phrase to use, because it brings up ideas of Spec Rel, with are completely irrelevant :/

Reply 12

k9markiii

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.

Reply 13

Qwertish

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.