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Homework Help: Generator problem

  1. Jan 10, 2013 #1
    Hello PF, I'm new here but I found you while googling around :> The forum seems great and has large activity, the only thing I miss is a chat function :p Anyways, I came here for some help regarding my physics essay, I'm in my second IB year (if you're familiar with this course) and need some help with the extended essay.

    This question is about wave power plants

    1. The problem statement, all variables and given/known data
    You have a coil of N turns spinning with the function x(t)=A cos⁡〖2π/T t〗
    Where A = 0,01 and T = (2π×0,01)/(-2π/6 1,6 sin⁡〖2π/6〗 t)
    yes, the period is messy :d If you question it, I retrieved it from this information:
    The waves will travels with the water as their medium, and there will be a deformation in pressure which will cause the buoy to oscillate.
    The waves in the water depend on the geographical position and the weather conditions, and therefore the idea will be tested on waves with different properties, and then compared to each other. This will be done in order to investigate how the electricity conducted will change as the waves change, as well as for which waves the idea will be optimal.
    For the first case waves found on the west coast of Sweden will be used. These waves have an average wave height of 1,6m and an average period of 6,0 seconds, and we can define our phase shift to be 0. which gives them the function:
    X(t)=1,6 cos⁡〖2π/6〗 t
    Or, for velocity of the wave:
    V(t)=-2π/6 1,6 sin⁡〖2π/6〗 t
    We know that the wave will move between +A and –A, which gives us ∆A=3,2m and it will make this change in half a period, 3 seconds. The generator will then spin with a function of ∆A/r 〖δt〗^(-1), where r is the radius of the axis. Since we want the generator to spin as fast as possible, and it will spin faster as r approaches 0, we want r to be as small as possible. However, there will be a limit where the friction won’t be enough to make the generator rotate, therefore a value of r will be chosen where there’s enough friction for the generator to rotate, and r is small enough to cause a high revelations per second. The value chosen for r is 1cm, which will be enough for the generator to spin as well as small enough for the speed to be high.
    The function showing the displacement of the generator is
    X(t)=A cos⁡〖2π/T t〗

    2. Relevant equations
    ℇ=-N dflux/dt
    Lenz' law

    3. The attempt at a solution

    BAcos(90cos 2π/(2πx0,01/(2π/6 1,6sin 2π/6 t)))=flux

    I use values 0,34T for B and 0,1m for A

    flux =0,034cos(90cos 2π/(2πx0,01/(2π/6 1,6sin 2π/6 t)))

    Problem is, I don't know how to use this information in order to find the relevant information about the current. My guess is that i should take the function for flux and shift it upwards with the amplitude and integrate it. And from there find the maximum emf and the "average" emf (squareroot(y(x)^2). But that'll give a DC current, which I don't have. So i should not shift it upwards and instead just integrate the function as it is? I'm lost :(

    P.S Linus, if you got an account here, and I bet you do, It's on its way :d
    Last edited: Jan 10, 2013
  2. jcsd
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