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    I don't understand that why the answer is C, and why am I getting n as 1.

    \phi = \frac{2\pi x}{\lambda}

    And taking \lambda to be equal to 1, x should be 0.5, and n is coming as 1. :confused:
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    Using your formula, x, the distance between X and Y is 1.5 wavelengths, so put x = (3/2) lambda in it and you get phi = 3 pi
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    (Original post by Stonebridge)

    Using your formula, x, the distance between X and Y is 1.5 wavelengths, so put x = (3/2) lambda in it and you get phi = 3 pi
    But what I read was that x IS always less than wavelength, and when any number of wavelengths come into the value of x we eliminate that number of wavelengths. Like for example let us take wavelength as 1, then distance between X and Y is 1.5, so eliminating one gives us 0.5 to be used as x? OR is my concept wrong? :s
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    Two points on a wave can be any number of wavelengths apart, and phi can be any value.
    I think what you are thinking of is the fact that, as the cycle just repeats itself, a phase difference of 1.5 wavelengths amounts to the same displacement as a difference of 0.5
    But a point at a phase difference of just pi would not be at the same place on the graph/wave as Y, though it is at the same distance below the axis, as will be the points at 2.5, 3.5 4.5 etc.
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    (Original post by Stonebridge)
    Two points on a wave can be any number of wavelengths apart, and phi can be any value.
    I think what you are thinking of is the fact that, as the cycle just repeats itself, a phase difference of 1.5 wavelengths amounts to the same displacement as a difference of 0.5
    But a point at a phase difference of just pi would not be at the same place on the graph/wave as Y, though it is at the same distance below the axis, as will be the points at 2.5, 3.5 4.5 etc.
    Hmm, though it's a bit difficult to understand but I'll try to remember it. Thanks.
 
 
 
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