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Functioning of AC current in simple terms?

  1. Jun 18, 2014 #1

    Thank you for reading this.

    I understand the functioning of DC current. You create a potential difference and the electrons flow from the power source through the electrical appliance (thereby, powering it) and flows back, completing the circuit.

    But, in AC, the electrons, according to what i read, move in one direction for sometime and then switch direction. And i read somewhere that there is no net movement.

    How does this work? I mean the electrons have to flow in one direction for them to reach the appliance, right? If they move forward and backward, how does it reach the destination?

    Please explain in simple terms.

    PS: I understand that my questions and my understanding of electricity may seem childish to people who know more than me.
  2. jcsd
  3. Jun 18, 2014 #2


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    Staff: Mentor

    Electrons move throughout the conductor when you complete the circuit, not just from the power source. Imagine the water pipes in your house. When you first turn on your hot water faucet, the water in the pipe nearest to the faucet comes out first, which is why it takes time for the water to warm up. You have to get that cold water that's been sitting there out first.

    In an AC circuit the electrons in the circuit move back and forth as a whole, including within the load device (the appliance).
  4. Jun 20, 2014 #3


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    Electrons in a wire flow incredibly slowly (an average speed of about 1mm per second) The energy flow from the Power Supply to the appliance is not at that speed. It is at a little less than the speed of light and is carried by an Electromagnetis Wave. (Think of the links of a cycle chain, which do not need to travel from pedal to back wheel before the bike starts moving.)

    A lamp may be lit and go off well before any of the electrons in the battery have actually got to the filament via the switch. Drakkith's hot water system explanation is an excellent one*** (although the water model is usually a risky one); the effect of turning on the tap is instant and long before the water from the source actually gets to the nozzle of the tap.

    With AC, the electrons in the wire change direction every few milliseconds and their mean position does not alter. You would never get any hot water from the system if you used and AC hot water supply but you could drive a hydraulic machine with pull push (AC) water supply pressure.

    ***Amazing that I have never come across that particular argument. It's a really good one amongst many really dodgy 'water' arguments.
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