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Current and voltage in AC

  1. Nov 14, 2011 #1
    I am sorry if this may seem like a beginner question (which I am not) but the I find the best way to learn something is to understand it from it's most basic components or operations first. In this spirit I have a question regarding the relationship between voltage and current in AC circuits. Voltage is defined as the energy required to move an electric charge from point A to point B (divided by the magnitude of the charge). In DC current when two wires are connected to the leads of a battery, the electron flow (not to confuse with the conventional current) is from the negative lead, or the most negative voltage to the positive lead or the most positive voltage. Along the way, the electrons move through the wire and dissipate their energy (voltage or eV) in the components they encounter in the circuit so when they arrive at the positive lead they will have no more energy or voltage. This part is clear. The thing I don't understand is in AC current. AC current being the come and go of electrons in the wire, they actually always end up in the position they started. I was wondering then, where does the voltage to move the electrons come from. In other words how is the voltage from the turbine at the electrical central transferred to the electrons present in the wall socket of my house since these electrons basically never reach the turbine. They seem to move forward and lose energy and then coming back losing some more in the other direction without recuperating it anywhere.

    Thank you

    I am sorry if it is not clear enough don't hesitate to tell me.
  2. jcsd
  3. Nov 14, 2011 #2
    Compare AC with waves on a string.Particles in string oscillate about their position but net displacement in a time period their net displacement is zero.Yet your energy gets transferred across string and even released if there is some damping(just as resistance in case of DC or AC circuits). However the energy to oscillate the string is given by you or the oscillator.Similarly the energy to oscillate electrons about their mean position is given by the turbine.
  4. Nov 14, 2011 #3
    What a silly contraption a bicycle is. All you do is move your legs up and down, around in a circle, how you you possibly get anywhere?


    Think about that a little bit, and you might get it.

    Here's another one. Press your hands together, and rub them back and forth. You're movig your hands back and forth in opposite directions, and yet you generate heat! They end up right back where they started, and yet work has been done.

    The final clue...

    Positive Voltage * Positive Current = Positive Power

    Negative Voltage * Negative Current = Positive Power

    Does it make sense now?
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