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Homework Help: Ring launcher conceptual question

  1. Apr 2, 2016 #1
    1. The problem statement, all variables and given/known data
    When an aluminum ring is placed on ring launcher so that it surrounds the coil, it flies upward when a AC current is applied to the coil. This does not occur when the intact ring is replaced by a split ring (see below). Explain this in 3 sentences or less. Feel free to use as many diagrams and equations as you need in your explanation. [Warning: The standard explanation of this lacks any mention of an essential feature.]

    2. Relevant equations

    3. The attempt at a solution
    This is my rationalization as to why this occurs:
    When the AC-current was turned on, the emf generated in the Aluminum ring led to a current in it, which according to Lenz's Law, has to be in a direction such that its field cancels the one due to the ring launcher: so it is opposite in direction and since opposite currents repel, the ring flies off. When a split ring is used, since it is not a closed loop, there is no flux going through it is 0. Hence, there is no emf or current generated: so it does not fly off.

    Did this go beyond the "standard explanation", as my Professor puts it? Or did I miss something "essential?"
    I have uploaded a picture of the figure (if it helps at all). I can only receive partial credit if my Professor isn't completely satisfied with the answer so if I'm missing something, I would greatly appreciate it if anyone could help steer me in the right direction. Thank you so much!

    Attached Files:

  2. jcsd
  3. Apr 3, 2016 #2


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    2017 Award

    Staff: Mentor

    Currents do not repel. There is something else that repels something.
    Going through what?
    One of them is generated.

    I don't know what exactly your prof means, but here is a question you did not answer: how does the ring know in which direction it has to go?
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