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Bulb problem

  1. Jun 20, 2007 #1
    The following diagram is of a setup consisting of
    A bulb
    A pair of wires...making an angle theta with the place the bulb lies in

    now if the setup is seen by an observer moving at a speed 'v' relative

    the angle the wires make with the plane changes to phi>theta(i can provide the equations to prove this if needed...i might hav gone wrong...but ive cheked it so far..)

    Now to the observer moving relative to the setup...the wires make a different angle...so what does that observer see?

    does he see the bulb giving off light..if he does..then from his point of view...there is no energy being provided ..so how does the bulb provide light....

    Last edited: Jun 20, 2007
  2. jcsd
  3. Jun 20, 2007 #2
    Those equations should also show that the bulb is now closer to the battery..
  4. Jun 20, 2007 #3
    Even though..theyr closer...wouldnt the width of the cavity containing the battry also contract...slo it wudnt make a difference...also the bulb's width would contract..
  5. Jun 21, 2007 #4
    please help!
  6. Jun 21, 2007 #5

    Doc Al

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    Staff: Mentor

    All linear dimensions along the direction of motion will "appear" contracted from the moving frame. Why do you think that that somehow implies that contact will be broken?
  7. Jun 21, 2007 #6


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    If you draw a right triangle with the wires as the hypotenuse, only the horizontal side of the triangle (the base) will be shrunk by length contraction, and it will be shrunk by exactly the same factor as the distance from the battery to the base of the bulb, so naturally the wires will still be in contact with the bulb. Different reference frames never disagree on local physical facts like whether two objects touch!
    Last edited: Jun 21, 2007
  8. Jun 21, 2007 #7
    but what about the change in the angle theta?
  9. Jun 21, 2007 #8

    Doc Al

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    What about it? Think of a ladder leaning against a wall at some angle. "Viewed" from a moving frame, the distance between the bottom of the ladder and the wall will be contracted. Of course it also appears to have a different angle with respect to the wall. (It better!)

    Everything (triangles included) "appears" narrower along the direction of motion.
  10. Jun 21, 2007 #9
    hmm...thnx..im getting it...

    thnx a lot
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