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    So, I was doing some synoptic revision, and came across something that confused me.

    Sin θc = 1 / n according to the formula sheet (AQA)

    as 1n2 = n2/n1,

    sin θc = 1 /(n2/n1) = n1/n2

    right?

    However, I did a past paper, June '02, and in the mark scheme, it says you work it out using the formula "sin θc = n2/n1"

    Please help me out here.
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    I'm guesing your talking about 3)b)ii)

    Core -> Cladding
    (n1 -> n2)
    (1.50 -> 1.32)

    1n2 = n1/n2

    = 1.50/1.32
    = 1.136


    critical angle is inverse sin of 1/n

    = 61.6

    -----------

    You always have to remember that Sin c must lie between 0 and 1, so therefore n will have to be greater than one - otherwise there will be no critical angle.

    MdSalih
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    (Original post by MdSalih)
    1n2 = n1/n2
    Why not 1n2 = n2/n1 as usual?

    It was 3) (b) (ii)
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    No it's n2/n1

    critical angle is when θ2 = 90
    sin 90 = 1...

    sin θ1 / sin θ2 = n2/n1

    therefore

    sin θc = n2/n1

    n2 represents the second refractive index
    n1 represents the initial refractive index
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    (Original post by corkskrew)
    No it's n2/n1

    critical angle is when θ2 = 90
    sin 90 = 1...

    sin θ1 / sin θ2 = n2/n1

    therefore

    sin θc = n2/n1

    n2 represents the second refractive index
    n1 represents the initial refractive index
    Ok, thanks, I suppose the formula sheet just gives sin θc = 1/n to be confusing then?
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    Actually that equations ok. Remember that "n" (the refractive index) is the speed of a wave relative to that wave in a vacuum. As air is condered to have n=1, for a wave travelling from glass into air...

    sin θ1 / sin θ2 = n2/n1

    therefore

    sin θc = n2/n1

    When going from glass to air, air is n2, so n2=1
    n1 is glass, so n1 =1.3 or whatever

    therefore

    sin θc = 1/n1
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    I always get confused with the n1/n2's and which to use, this info has been helpful thanks!

    Also, Mdsalih did you used to hand around in planetarion irc? sure ive seen you somewhere....
 
 
 
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