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AC voltage source

  1. Feb 3, 2010 #1
    What does it mean when you put on a AC voltage source (~) 50/60º.
    The book i've been studying from says the rms or peek voltage only.
    Thanks.
     
  2. jcsd
  3. Feb 3, 2010 #2

    vk6kro

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    AC voltages are usually given as the RMS voltage and the frequency.

    The household supply varies with different countries, but most fall into the 100-120 volt 60 Hz frequency group (North America, Japan), or the 230-240 volt 50 Hz group.

    The supply is always a sinewave and the RMS value is the peak value divided by 1.414.

    This site:
    http://en.wikipedia.org/wiki/Mains_power_around_the_world
    gives an interesting look at the mess of voltages and plugs around the world.

    50 Hz / 60 Hz means that either 50 Hz or 60 Hz is OK.
     
  4. Feb 4, 2010 #3

    sophiecentaur

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    An AC waveform, at least from the mains, is sinusoidal. The power delivered is an average over the whole cycle of Voltage, which goes from + peak, through zero, to a - peak. The average value of Voltage is zero - which doesn't tell you much about the peak values. To work out the 'effective' Voltage to get power delivered to a load, you need to add up (integrate) the energy delivered at all stages in the waveform.
    One formula for power is P =V2/R.
    If you average this over the whole cycle for all instantaneous values of V and average it, you get the 'mean square' value of the Power. Rearranging and taking the square root of this gives the 'Root Mean Square' (RMS) value of the varying Voltage. For a sinusoid, the RMS value is the peak Voltage/(Root 2). The relationship is different for other shapes of waveform.
    This RMS Voltage produces the same power from a resistor (lamp / heater etc.) as a DC Voltage of the same value.
     
  5. Feb 4, 2010 #4
    For many AC circuits, whether the frequency is 50 or 60 Hz is of little consequence. But in circuits that have transformers, use of 50 Hz AC power in a transformer designed for 60 Hz at the same voltage will exceed the volt-seconds of the iron core and drive it into magnetic saturation.

    Bob S
     
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