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Homework Help: Rms voltage question

  1. Dec 1, 2007 #1
    1. The problem statement, all variables and given/known data
    Hi, so im just starting an rms voltage question but i'm a small bit confused.
    The problem states: A transformer having 90 turns on the primary and 2250 turns on the secondary is connected to a 120V, 60Hz source. Calculate a) the rms voltage and b) the peak voltage at the secondary.

    2. Relevant equations
    Vrms = Vm/2^0.5

    Ns/Np = Vs/Vp

    3. The attempt at a solution
    So far i have said:
    Vs = (120)(2250)/(90) from the second equation above
    => Vs = 3000V

    After this i was going to say that the rms voltage is Vs/2^0.5
    however i have been given the answer and it says that the rms voltage is simply 3000V. I dont understand this and would appreciate any explanation any one could offer?
    I realise i also havent used the 60Hz value,so i may be missing an equation??
    Thanks for any help
  2. jcsd
  3. Dec 1, 2007 #2


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    Science Advisor
    Gold Member

    Your Vs is the secondary rms voltage because it was calculated from an rms primary value. So far so good. The frequency is unimportant except to indicate that you are working with AC (alternating current), which means a sinusoidal waveform. To finish the problem and calculate the peak voltage, what do you know about the relation between peak and rms amplitudes for a sine wave?
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