What Voltage?

Discussion in 'Homework Help' started by JDR04, Jul 16, 2012.

  1. JDR04

    Thread Starter Active Member

    May 5, 2011
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    Could somebody please help me with this question. I stated that the attached combination of 1.5V cells would read 0V because the extreme left hand cell is reversed. My tutor marked it wrong.

    Could somebody tell me what the correct answer is and why so I will understand it better.

    Many Thanks - JDR04
     
    Last edited: Jul 16, 2012
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The picture is to small to make it out.
    Can you post a larger one?

    Bertus
     
  3. bretm

    Member

    Feb 6, 2012
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    Only one of the four cells is reversed. This will cancel one of the three other cells, leaving a net of two cells, and 1.5V x 2 = 3V.
     
  4. JDR04

    Thread Starter Active Member

    May 5, 2011
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    Hi bertus, I've attached a bigger image, thanks for your time - JDR04
     
  5. JDR04

    Thread Starter Active Member

    May 5, 2011
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    Hi bretm, thanks for the info. I'm really confused now. I was under the impression the electrons could only flow from negative to positive so if I measured across these 4 cells which are all connected in series, I would be measuring from a negative terminal to a negative terminal. What am I missing?
     
  6. Adamf001

    Member

    Sep 5, 2011
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  7. bretm

    Member

    Feb 6, 2012
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    Slight side track here--ignore if you want--but electricity is not flow of electrons. The only reason I bring this up is because batteries are the most common counter-example. Charge flow in chemical batteries often consists of the flow of entire atoms, and in many cases this involves positive ions (atoms missing one or more electrons) which would tend to flow from positive to negative inside the battery, but who's net motion is a combination of this coulomb force and the force of the chemical density gradient.

    Really, though, ignore that whole paragraph if you don't care about that stuff because it's not directly related to your comment which seems to refer to the electron flow in the circuit external to the battery.

    A given location in a circuit, such as a battery terminal, is neither positive nor negative. It's only positive or negative in relation to some other point in the circuit. In this case, one end of the of series batteries is more negative than the other end, so that's the "negative terminal", and the other end is the positive terminal.
     
  8. #12

    Expert

    Nov 30, 2010
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    Now that we have somebody on this site that refutes electron flow theory, I'll try to simplify this. The question was, "What is the voltage" not, "what is the current". You don't even have to believe in electrons to see that 1.5V +1.5V +1.5V -1.5V = 3V whether electrons flow or not.
     
  9. bretm

    Member

    Feb 6, 2012
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    If you're referring to me, I don't think you read my post very well. I clearly delineated the part of the post that was an aside, and nowhere did I "refute electron flow theory".
     
  10. JDR04

    Thread Starter Active Member

    May 5, 2011
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    Thanks Adamf001, handy info.I'll go through it. JDR04
     
  11. JDR04

    Thread Starter Active Member

    May 5, 2011
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    Thanks bretm, thanks for your input.
     
  12. JDR04

    Thread Starter Active Member

    May 5, 2011
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    Thanks, when you put it like that I kind of kicked myself. Thanks a lot-JDR04
     
  13. #12

    Expert

    Nov 30, 2010
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    bretm, this is the part that bothers me. I've had my caboose kicked thoroughly on another site by people that don't believe in electron flow. This site does at least seem to believe that electrons flow and they are the charge carrier in common, everyday circuits. It frightens me that the same argument might start up on this site, partly because I believe electrons flow and partly because this is a teaching site and it will confuse the noobies if you tell them that electricity is not (the) flow of electrons.
     
  14. takao21203

    Distinguished Member

    Apr 28, 2012
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    And what will the reverse current do to the other batteries?

    Any real-world measurement?
     
  15. bretm

    Member

    Feb 6, 2012
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    Not being a crackpot, just pointing out that electricity is the flow of charges in general, not just electrons. Often those charges are electrons, but the subject was batteries so I just pointed out that in batteries the charge often isn't electrons, but positive ions. I realized it complicated things so I went to lengths to put it in a side comment, which is hard to do well in this format.
     
    Last edited: Jul 17, 2012
  16. bretm

    Member

    Feb 6, 2012
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    It depends on the battery chemistry. Careful application of reverse current can charge a rechargeable battery. Other types can explode.
     
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