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Homework Help: Lamp moving at v=c/4

  1. Apr 26, 2016 #1
    • Thread moved from the technical forums, so no HH Template is shown.
    Hello, I need help with this problem. In 2D we have a lamp that emits light in 360 degrees around itself while stationary. Than it starts moving at velocity of c/4 what is the degree of the cone in which the light now emits to ? I hope you understand, like the angle of the field where the light falls from the perspetive of observer who is stationary. I dont know how to solve it, does anebody know ? IMG_20160426_215423.jpg
    Thank you Radim
  2. jcsd
  3. Apr 26, 2016 #2


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    Consider a photon emitted directly to the left when the source is stationary. In what direction will it travel when the source is moving?
  4. Apr 26, 2016 #3


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    Light is still being emitted in all directions, with Doppler shifts.
  5. Apr 26, 2016 #4
    Yes you are correct, I misunderstood the problem, it made no sence to me that the light would not be emitted to the left from the stationary observers perspective. They are asking for angle of beams of photons that were emitted perpendicular on the vector of velocity (but they won´t be perpendicular while it is moving) The answer is supposed to be 152 degrees, but I dont know how they got this result.

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  6. Apr 26, 2016 #5


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    The phenomenon is called "aberration", and occurs in both Newtonian and relativistic physics. Google for relativistic aberration.
  7. Apr 26, 2016 #6
    So could anyone confirm me that this approach is correct ?
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