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Homework Help: Relativity - world lines

  1. Jan 11, 2014 #1
    1. The problem statement, all variables and given/known data
    A light source at the origin of the O frame emits short pulses of light in interval of [itex]\tau[/itex] as measured in O. An observer located at the origin of the O' frame which moves at velocity v with respect to O along the x-axis, receives these light pulses.
    Use a world line diagram to show the receipt of two consecutive pulses as measured in O if the first is emitted when the frame origins coincide. Show that measured in O the pulses are received at the origin of O' with the temporal separation of (c[itex]\tau[/itex])/(c-v) and spatial separation of (c[itex]\tau[/itex]v)/(c-v).

    2. Relevant equations

    3. The attempt at a solution
    The pulses of light travel at velocity c
    The receiver travels at velocity v
    I have drawn the world line (t-x plot) and I'm pretty sure it's Δt and Δx i need to calculate but i'm not sure how to go about it.
    http://img24.imageshack.us/img24/4083/z559.png [Broken]
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Jan 11, 2014 #2


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    Your diagram looks good. Now you're trying to find where the two lines intersect. This is just like what you did in algebra class, except this time the variables are x and t instead of x and y.

    Start by figuring out the equations for the two lines.
  4. Jan 11, 2014 #3
    I didn't realise it would be so simple, thanks a lot for the help. It worked out perfectly.
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