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Discuss Can you work out the value of the resistor? in the Electrical Forum area at

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  1. thepipersson198

    thepipersson198 Guest

    Hi guys,

    Just wondering if you can help me on this one,

    I have a RLC series circuit the values are as below;

    R = unknown
    L = 800mH
    C = 300uF

    from there I have calculated;

    the resonant frequency to be 10.3Hz
    the capacitive reactance 51.50 ohms

    The reason I need to know is I need to work out the impedance, which is

    Z= sqrt^R^2+(Xl-Xc)^2

    So I have the following,

    R is unknown
    L is 800mH
    C is 300uF
    F = 10.3Hz
    W = 2pie*F
    Xc = 1/WC
    Xl = WC

    So If there is a way i could work out what the resistors value is, then I can work out what the impedance is, but please bear in mind this is just a paper exercise, so I have no tools i can use to determine this for me.

    Many thanks for your help in advance
  2. Marvo

    Marvo Admin and gender confused Staff Member Admin

    South Africa
    If you're currently on a training course you can get access to our Trainee section which you might find helpful.

    Check out this thread, do the necessary and access will be granted if you qualify.
  3. Lucien Nunes

    Lucien Nunes Mercury Arc Rectifier Respected Member

    You have too many unknowns. If you knew the resistor value you could calculate the impedance at a given frequency, or vice versa, but at the moment you have neither so cannot calculate anything.
    • Like Like x 1
  4. happysteve

    happysteve Electrician's Arms

    Business Name:
    Dovecote Electrical
    Do you know the Q factor of the resonant circuit? If so, you could work out R using:

    Q = (2 x pi x f0 x L) / R

    ... or ...

    Q = 1 / (2 x pi x f0 x C x R)

    (where f0 is your resonant frequency)
  5. uksparks

    uksparks Electrician's Arms

    Market Harborough
    I thought the coloured rings around resistors were to tell you how much is was?

    • Like Like x 2
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