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Direction of Current in AC circuits.

Discussion in 'General Electronics Discussion' started by electronicsLearner77, Oct 6, 2020.

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  1. electronicsLearner77

    electronicsLearner77

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    Jul 2, 2015
    I am confused with the direction of current for AC circuits, for example if i consider the below circuit
    upload_2020-10-6_13-13-41.png
    My main concern here the direction of current is shown going from -Ve to +Ve and the source is the AC signal.
    Q1. Will the direction of current will always be the same as shown in the figure?
    Q2. During the negative region of the sine wave the current direction changes and starts flowing from +Ve to -Ve and it keeps alternating for every half cycle? I don't understand it, i am missing the basics.
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    In AC circuits the current constantly changes direction, as indicated by the name AC = Alternating Current. Showing "+" and "-" on an AC source is misleading. Best to ignore these labels.
    The arrows are used to indicate current flowing from the source through the load back to the source. If this current is positive (positive half of the sine), voltages are equivalently positive. During the negative half of the sine voltages are equivalently negative.
     
  3. electronicsLearner77

    electronicsLearner77

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    Jul 2, 2015
    Yes i understand this i ignore it.

    Can you please confirm if the current upload_2020-10-6_20-2-4.png keeps changing direction every half cycle or it is always in the same direction shown in the original diagram.
    upload_2020-10-6_20-7-8.png
    Now i have removed the "+" "-" signs. But also can you please confirm if ground connection will be there or to be removed, as I am confused with ground connection as well? Very confused, please help, I am mixing everything.
     
  4. Minder

    Minder

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    The Earth ground symbol in this context has no meaning.
    In the true definition of the symbol, it is irrelevant.
    This just indicates that one side is referenced to earth ground.
    In normal practice termed 'Neutral'.
    M.
     
    hevans1944 likes this.
  5. electronicsLearner77

    electronicsLearner77

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    Jul 2, 2015
    But in any circuit design we should have ground or reference.
     
  6. Minder

    Minder

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    If this is just a common reference then use the correct symbol.
    See Dr Archambeault's comment!.
    In actuality, in your diagram there is no real need for a common reference point.
    M.
     

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    Last edited: Oct 6, 2020
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  7. electronicsLearner77

    electronicsLearner77

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    Jul 2, 2015
    Can you also please explain the other question i asked about the direction of current.
     
  8. bertus

    bertus Moderator

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    hevans1944, Minder and Harald Kapp like this.
  9. Bluejets

    Bluejets

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    It's no wonder you have trouble understanding as it seems you do not follow the answers.
    Harald described it quite clearly in the first sentence of his reply #2.
     
  10. electronicsLearner77

    electronicsLearner77

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    Jul 2, 2015
    If I don't understand I have to say I did not understand. I know the answers are given but it does not mean I understand them at one go, I need to get clarity to convince myself. I appreciate the support and time you people are spending.
     
  11. hevans1944

    hevans1944 Hop - AC8NS

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    This is NOT a true statement. The use of "ground" whether it be an "Earth ground" or a power-line "neutral ground" or a "reference ground" or any other kind of ground has absolutely no purpose in any circuit design other than as one of a pair of points between which electrical potential can be measured... for whatever purpose the designer desires or for no purpose at all.

    Your incorrect statement can be disproved with just one counter-example, although there are many other counter-examples. The first one that comes to my mind is a simple hand-held flashlight consisting of a case, a battery, a lamp or LED, and a switch to turn the lamp or LED on and off. The battery, lamp or LED, and the switch are connected in a series circuit design with nary a "ground" anywhere in sight.

    At this point in your learning, the ONLY thing you need to know about "ground" is this: ALL points identified as being the SAME "ground" will have ZERO potential between them. Such a collection of "ground" points may or may not be identified as such on a schematic, but any one of them is a reference point for measuring potentials in a circuit with respect to "ground."

    In the real world there are many types of "ground". The terminology is ancient, going to at least as far back as the days when land-line telegraphs had just one wire strung between telegraph poles and a second wire (to complete the telegraph circuit) buried in the ground at each end of the single telegraph wire. This saved a fortune in not having to string a second copper wire along with the first one, just to complete the telegraph circuit. However, if money were no object, a second wire could have been strung and the telegraph would work just fine without a connection to ground.

    In modern electronics, significantly different currents can flow in different parts of a circuit. Analog circuits typically use much smaller currents than digital circuits, and digital circuits typically create large current transients as a result of fast switching activities. These currents create voltage drops in conductive board traces that are nominally all at the same potential. The high current traces are sometimes identified as power supply common, power supply ground, or digital common... all of these expressions being used to mean a high-current common.

    For the purpose of measuring voltages (potentials) in circuits with respect to power supply common, power supply ground, or digital common, the small voltage drops (millivolts) in the board traces can often be ignored. However, these voltage drops can wreak havoc in measuring sensitive (microvolt) analog signal circuits. To prevent this, the sensitive analog circuits have their own power supply common, analog common, that is separate from the higher current traces. The analog circuits may even have their own isolated analog power supply, but eventually the analog signals (after amplification and other conditioning) may need to interface with the higher-powered circuits. The simplest way to allow this to happen is to connect the analog circuit common to the digital circuit common at a single point (called a "star" connection). Usually the schematic will separately identify analog common from digital common, usually with a triangle symbol with a number inside the triangle. The "star" connection is where the two meet.

    You may ignore the three previous paragraphs until you encounter circuits that actually NEED two or more "grounds."
     
    Minder likes this.
  12. ratstar

    ratstar

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    Aug 20, 2018
    god i hate electronics notation, cant understand anything from it.
     
  13. Ratch

    Ratch

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    In determining the physical direction of current you have to know two things, the polarity of the the voltage and the polarity of the charges that make up the current. In 99.44% of the cases, the charges are electrons which carry a negative charge. So, the physical current direction is from the negative terminal to the positive terminal of a battery or any electrical voltage supply. This is true regardless of what is designated "earth" or anything else. If you are dealing with a proton circuit, then the opposite would be true, because protons have a positive charge and are repelled by a positive voltage, get it? When doing electrical calculations, it more convenient to ASSUME that charge flows from positive to negative because it eliminate all kinds of pesky negative signs and mistakes in the calculations. But, when the results are obtained, the direction of the calculated current is reversed if the REAL physical direction of the current has to be known.

    One other thing. Saying "current flow" is poor English. It literally means "charge flow flow". You should instead say "charge flow", or just plain "current", or "current is present" or "current exists", etc. In other words, current already indicates charge flow. Ratch
     
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  14. Harald Kapp

    Harald Kapp Moderator Moderator

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    But common use.
    AS is LCD display which literally is a Liquid Crystal Display display.
    Language isn't always concise. We've had this particular discussion before.
     
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  15. Ratch

    Ratch

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    While not exclusively solidly crystalline or sloppy liquid, LCDs do exhibit characteristics of both types of materials. (https://en.wikipedia.org/wiki/Liquid_crystal)

    Saying "current flow" is like saying "low-fat buttermilk" or "low-fat skim milk", or "non-cholesterol vegetable oil". It is redundant and ridiculous and there is no excuse for it. Ratch
     
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  16. hevans1944

    hevans1944 Hop - AC8NS

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    How language is formed and used doesn't NEED an excuse, the Hopelessly Pedantic being excused from this discourse. Still, it's nice to see @Ratch is still alive and kickin' butt as per usual. I, for one, will continue to say "the Sun is shining, the Mississippi River is flowing, and current is flowing in my circuits. How do I know all these things? I have an obsolete photocell film-camera light-meter that will tell me how much sunshine there is, I can dip my hand in the river to feel the river flowing by, and I have this spiffy multi-meter that manages to measure the current in my circuits, and whether that current is flowing or not.

    As for low-fat or non-cholesterol anything, I try to avoid those things and go for the gusto: real Vermont cultured and churned butter, Angus rib-eye steaks, 100% whole milk, and of course all of those things in moderation. I love mayonnaise on my hamburgers, but never on my French-fried potatoes: I make gravy for that, using butter, Angus pan drippings, and a mix of almond flour and Gold Medal white flour, sometimes with a dollop of bacon grease to add more flavor and robustness.:D
     
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  17. ratstar

    ratstar

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    Aug 20, 2018
    Thats enjoying your cuisine!
     
  18. davenn

    davenn Moderator

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    OK guys

    the original Q has been well answered
    Time to close the thread before it gets totally off course :)
     
    hevans1944 likes this.
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