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How do the appliances work with AC voltage?

  1. Aug 11, 2015 #1
    how do the appliances work with AC voltage when the polarity keeps changing?
     
  2. jcsd
  3. Aug 11, 2015 #2

    anorlunda

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    Think of a resistance load. For the first half of an AC cycle voltage is plus and current is plus. Power is voltage times current, thus plus. In the second half of the cycle voltage is minus and current is minus, but voltage times current is still plus. (-1 * -1 = +1). So the directin of power flow is the same through the whole cycle.
     
  4. Aug 11, 2015 #3

    BvU

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    And for motors look e.g. here

    And: Hello, Aditya, welcome to PF :smile: !
     
  5. Aug 11, 2015 #4

    davenn

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    primarily, because in general, AC appliances are not polarity conscious ... that is, they don't need a specific + and - supply like from a battery


    Dave
     
  6. Aug 12, 2015 #5

    meBigGuy

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    A light bulb does not care that the voltage is changing and polarity is reversing because it has a slow response time.

    For systems that are sensitive, the AC is converted to DC. In fact, that is true for most appliances (other than toasters, heaters, AC motors, etc).

    There is nothing in your TV that runs off the AC directly. It is converted to many different DC voltages. Same for your Computer.
     
  7. Aug 12, 2015 #6
    Then you mean to say the current keeps changing its direction?
     
  8. Aug 12, 2015 #7

    davenn

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    yes. that's its definition .... AC = Alternating Current :smile:



    Dave
     
  9. Aug 12, 2015 #8
    Well
    Well then how can an appliance handle such kind of a thing when the current in the circuit keeps changing its direction?
    That was my initial question.
     
  10. Aug 12, 2015 #9

    meBigGuy

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    Did you read my reply? #5
     
  11. Aug 12, 2015 #10
    Yes I think you are right. Thanks :)
     
  12. Aug 12, 2015 #11

    meBigGuy

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    It doesn't matter that I am right :smile:, does it fully explain what you wanted to understand?

    In order to efficiently transform voltages you need AC power. The changing currents allow one to use transformers to efficiently change voltage without power loss. For example, 110VAC 0.1 Amp (11 watts) applied to a proper transformer would power a circuit that requires 5VAC 2.2A (also 11Watts). That ease of voltage transformation is one thing that make AC very useful. Then, after transforming voltage, there are very simple techniques to convert the AC to DC, which most electronic circuits require.

    Your PC power supply (and most wall-wart chargers) do this to an extreme. They convert 110VAC/60Hz directly to DC and then chop it back into AC at high frequencies (100KHz or higher) to put it through a transformer that creates many AC output voltages. Then they convert those back to DC, say 5V, 12V, and 3.3V to power a PC. For various other reasons, creating 100KHz AC allows efficient power transfer through a cheaper, smaller transformer.

    So, AC is not a problem for appliances, it actually makes it easy to transform the power to voltages needed by an electronic system. Most don't actually run on AC internally.
     
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