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What's the Difference Between Positive and Negative?

  1. Apr 13, 2016 #1
    I am aware of what positive and negative polarities are but what specifically causes the distinction between positive and negative polarity?
     
  2. jcsd
  3. Apr 13, 2016 #2

    berkeman

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    Welcome to the PF.

    What is the context of your question? Polarity of what? Of a capacitor or a resistor, as in electronics? Or as charge on particles?
     
  4. Apr 13, 2016 #3
    Charge on particles specifically. For example electrons and protons are negative and positive respectively but these are simply names. What is different about a protons positive charge to an electrons negative charge?
     
  5. Apr 13, 2016 #4
  6. Apr 13, 2016 #5

    sophiecentaur

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    There may be a very simple answer to satisfy you.
    Early experiments with rubbing glass etc. with fur etc. ( you know the sort of thing) found that some combinations of charged objects attracted and other combinations repelled. The results were looked at and it was concluded that there must be only two kinds of electric charge. They could have been called anything - Red and Blue, George and Harry but the Maths involved when using just 'names' would have made life very hard. It was decided that the charges could best be described by a value (how much charge or how much force etc) and a sign. The choice of which sign to choose for a charged glass rod or a charged piece of amber or from one particular terminal on an early chemical battery was quite (afaik) arbitrary. This was way before they discovered charged sub-atomic particles like electrons and protons. When the electron was discovered and its charge measured, it came out as -1.6021766208(98)×10−19coulombs - and they're all the same.
    This negative value of the electronic charge is absolutely fine (really!!!) but it does confuse and upset students because the flow of electricity in metals (and most other things) consists of electrons (negative charges) flowing from the Negative Terminal to the Positive Terminal.
     
  7. Apr 13, 2016 #6

    Averagesupernova

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    Hey I can't help but rattle your cage on this. I looked and looked but couldn't find any polarized resistors in my collection. :headbang: LOL
     
  8. Apr 13, 2016 #7

    sophiecentaur

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    There's always ONE, isn't there. :H
     
  9. Apr 13, 2016 #8

    berkeman

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    LOL. I meant it in the context of the + and - sides of the resistor that has a DC current flowing through it. :smile:

    The question was originally in the New Member Introduction forum, so there was no context at all to try to guess what polarity the OP was asking about. First I moved to EE, and then finally to GP when the OP finally answered with the context.
     
  10. Apr 13, 2016 #9

    Averagesupernova

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    You know I am not above learning something. I thought maybe there was something about resistors that I did not know yet. :smile:
     
  11. Apr 14, 2016 #10

    Svein

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    The Greek word for amber is electron...
     
  12. Apr 14, 2016 #11
    It has too do with current in the circuit the resistor is found in. And the reference point for identifying the polarity is the power source. The end of the resistor that is connected to the negative terminal of the battery is negative when the other end is connected to the positive terminal of the battery.
     
  13. Apr 14, 2016 #12

    sophiecentaur

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    The choice of the sign was long before the electron was found and named. The name was fitted to the fact, in retrospect.
     
  14. Apr 14, 2016 #13
    It seems the source of electrons was determined and labeled Negative and home was labeled positive. As mentioned previously heating metal in a vacuum produces an electron cloud without anything being connected to it. Putting a piece of metal close to the cloud and connecting the hot plate to the cold plate caused electrons to migrate to the cold plate to return home through the conductor. This caused an electric current in the connecting conductor. Connecting a battery negative terminal to the hot plate and positive to the cold plate enhanced the electron flow. Reversing the connection stopped the flow.
     
  15. Apr 14, 2016 #14

    sophiecentaur

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    Hang on a bit. They hadn't discovered electrons (and didn't know much at all about Electricity) when the + and - signs were allocated to the batteries that they made. They had no real idea about the Chemistry of how the batteries worked.
    Your are post hoc rationalising the situation. If 'they' had decided to call the metal electrode of a Leclanche cell "positive" then it would have turned out that the electron was a positive particle- once it had been found.
     
  16. Apr 14, 2016 #15

    sophiecentaur

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    Also, what they saw was referred to "Cathode Rays" and it was not identified as a stream of particles until even later.
     
  17. Apr 14, 2016 #16

    anorlunda

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    The "they" was Benjamin Franklin. He was the first to label the poles positive and negative. https://en.wikipedia.org/wiki/Benjamin_Franklin#Electricity

    If we ever invent a time machine, Franklin's choice of which pole was negative would be one thing I would love to change. (Just as cosmologists would love to uninvent the phrase "Big bang", and QM physicists would like to choose a different word than observable.)
     
  18. Apr 14, 2016 #17

    sophiecentaur

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    Yes, on the face of it but having electrons with a negative charge does make people stop and think and it must help to discourage the very Mechanical picture that people risk getting in their heads about Electricity.
    I wonder whether any well informed PF Chemists could suggest a better than arbitrary reason for the signs. Could it be anything to do with Adding or Subtracting some element in an electrolytic cell - like you get Hydrogen 'taken out of' water at the (-) Cathode?
    Just a whimsical thought but there would have to have been some basis for the choice - if they could have possibly found one.
     
    Last edited: Apr 14, 2016
  19. Apr 14, 2016 #18
    It seems like arbitrary labeling is based on the triboelectric charge and its behavior relative to objects around it. Imagine working with lightning instead of Amber. A powerful electron spark will leave a small pit on polished graphite if the graphite is positively charged with respect to the source of the spark.
     
  20. Apr 14, 2016 #19

    sophiecentaur

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    And where would the early workers have got hold of a controllable "powerful electron spark" if they didn't know about electrons? You can't use modern arguments if you want to put yourself in the shoes of ancient Scientists.
     
  21. Apr 14, 2016 #20

    anorlunda

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    I know that each country's education tends to focus on its own national heroes. But can it be that you never heard of Franklin's kite and key, and Leyden jar Sophie?

    pt1-10.jpg
     
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