Speed of light is constant in a particular medium

Discussion in 'Physics & Math' started by Saint, Nov 1, 2020.

  1. Saint Valued Senior Member

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    Will speed of light vary in different medium?
    In vacuum, air, water?
    Is that difference significant?
     
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  3. exchemist Valued Senior Member

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    The phase velocity of light changes significantly when it passes from a vacuum into air or from air into water. That change in velocity is what leads to refraction.
     
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  5. Janus58 Valued Senior Member

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    Significant in what way?
    In terms of Relativity, no. Relativity is based on c being invariant, which is the speed light travels in a vacuum.
    So for example, in a vacuum, two observer moving relative to each other will both measure the same beam of light as moving at c relative to themselves.
    In water however, this would not be the case. Someone as rest with respect to the water would measure the speed of a beam light moving at one speed relative to himself and someone moving at v relative to the water would measure a different value.
    But even in this case, c is instrumental.
    For the person at rest with respect to the water measures a speed of c/n, where n is the index of refraction. The other observer will measure a speed of (v+c/n)/(1+v/(nc))*

    *Velocity addition formula is w = (v+u)/(1+ vu/c^2). In this case, u = c/n, which causes the equation to reduce to the above form.
     
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  7. James R Just this guy, you know? Staff Member

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    Does it ever occur to you to google something before you post your question here?

    Are you asking people's personal opinions? Define "significant" in this context, please.
     

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