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Simple Battery Explanation

  1. Jul 28, 2012 #1
    Just a bit confused & I am in need of a simple explanation of how energy flows in a battery. This was my thinking:

    Cathode: positive terminal, current flows OUT
    Anode: negative terminal, current flows IN

    Is this correct? And if so, why do many battery diagrams depict energy flowing out the anode?

    As here: http://www.electrical.com/how-batteries-work/
     
  2. jcsd
  3. Jul 28, 2012 #2
    You have to specify whether 'current flows out' means out into the external circuit or internally within the battery....I assume you mean the former?

    When electricy current flow was first studied, nobody knew about electrons....so the initial convention used was about positive ions.....or protons moving around...THAT convention is often used still and shows [positive, conventional] current flow out of the positive terminal into the extrernal circuit.

    You can pick either convention to use....the difference is then one of sign [plus, minus] in formulas.

    edit: I see wikipedia discusses this:

    "An anode is an electrode through which electric current flows into a polarized electrical device. The direction of electric current is, by convention, opposite to the direction of electron flow. In other words, the electrons flow from the anode into, for example, an electrical circuit. Mnemonic: ACID (Anode Current Into Device)."

    http://en.wikipedia.org/wiki/Anode

    Sometimes this nomenclature really gets confusing: In salt water, for example everybody calls 'cathodic protection' connecting zincs in special 'bonding circuits' to protect against corrosion; yet discussions usually refer to zinc ANODES.....
    So when you are thinking about ions moving in salt water to complete a circuit, you have to be aware of what is actually happening as some ions are positive and some negative.....and they flow in opposite directions to each other.
    you say potato, I say potato....
     
    Last edited: Jul 28, 2012
  4. Jul 28, 2012 #3
    Ah! Yes. And herein lies the reason for my confusion. I supposed I'm referring to electric current then but the diagrams are, of course, showing electron flow (which is opposite). Is that correct?
     
  5. Jul 28, 2012 #4
    Oh, I also notice Wikipedia discusses the 'confusion' I mentioned....

    from the above wikipedia article....

    pick any Mnemonic you like to remember this confusing terminology.....
     
  6. Jul 28, 2012 #5
    Thank you for your help!
     
  7. Jul 28, 2012 #6
    Scientists refer to both as "current". However, the flow of positive charges is sometime specified by the term "conventional current". I have heard the term "electron current" is occasionally used to specify the flow of negative charge.
    You are talking about conventional current, while the diagram is showing "electron current". Some textbooks claim that "conventional current" should be the default meaning of current. From what you told us, some writers consider "electron current" to be the default meaning of "current".
    Your textbook writers may treat the meaning of "current" as a context sensitive default. The assumption of many writers is that the reader knows the physical principles cold. Therefore, the reader can infer what specific convention to choose from the context of the first paragraph or from the diagram. Your diagram shows the flow of electrons. If the writer is self consistent, he should present the equations and wording consistent with "electron current".
    Some writers are not consistent. I treat every use of the word current as a context sensitive default. That is, I always try to track what convention is being used from the local context while I read a chapter or article. If the writer makes a slips, or intentionally shifts gears, then I am ready. In the case of current, it isn't too hard to monitor context.
    The defaults on the word "current" are relatively easy. One heads up. The convention becomes really important when the hand rules are presented. However, writers are usually try to be consistent when they use the word "current". I will shift to a related topic, while you aware of the problem.
    Scientific jargon in general has ambiguities that are solved by convention. However, textbook writers sometimes don't assign a default meaning to a word. This creates confusion. For instance, there are several discussion threads going on right now concerning thermodynamics.
    Thermodynamics has one of the worse ambiguities in jargon that I have ever seen. The word "heat" sometimes refers to "energy" and sometimes refers to "entropy". That is something that used to throw me every other time the word 'heat" was used. There is no formal default for the word "heat". Every time the word "heat" is used without a qualifier, I have to decide which meaning to use based on context alone. This is not really an ambiguity in the physics, but a problem in jargon.
     
  8. Jul 28, 2012 #7
    Darwin123, you bring up a very good point. Given that, I feel the writers should give us qualifiers when describing current (& heat for that matter).

    Since you've brought it up, how does the right-hand rule play into this concept of current? I like to tie it all together.
     
  9. Jul 28, 2012 #8
    The positive terminal is the Anode. The negative terminal is the Cathode,
    Conventional current is a 'convention' in science, it is not something decided by writers. It is the direction in which + charges would flow.
    Electron current should be made clear by writers if that is what they are talking about.
    All of the rules in magnetism rely on the CONVENTION
    This has got nothing to do with heat or entropy.... dont get confused
     
    Last edited: Jul 28, 2012
  10. Jul 28, 2012 #9
    Now I'm confused again. The diagrams (including the one in the above link) have the positive terminal labeled as the Cathode.
     
  11. Jul 28, 2012 #10

    davenn

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    yeah I was looking at that pic in the link bbgirl showed and was thinking thats not right

    going back to my good ol' valve (electron tube ) technology electrons flow from Cathode NEGATIVE to the Anode POSITIVE
    its the ANODE that has the large positive voltage on it, not the cathode

    Dave
     
  12. Jul 28, 2012 #11
    Now I'm back where I started when I posted this. Totally confused.:confused:

    All the diagrams I've found show the electrons flowing the same way as the one I've linked above with the cathode labeled as the positive terminal. Are you saying they're all wrong?

    Can someone post a correct diagram that we can agree on?
     
  13. Jul 28, 2012 #12

    OmCheeto

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    http://www.electrical.com/wp-content/uploads/2011/08/battery.gif [Broken]

    That's the way I learned it the first time.

    But then again, wiki shows this:

    260px-Ohm%27s_Law_with_Voltage_source.svg.png

    But they also show this:

    230px-Current_notation.svg.png

    I know this all sounds [STRIKE]retarded,[/STRIKE] [STRIKE]mentally challenged,[/STRIKE] [STRIKE]differently abled,[/STRIKE] retarded, but that's just the way the world is.

    I've been told that engineers, the ones who design the world we live in, use hole flow(from + to -), and that technicians, the ones who build the world we live in, use electron flow.

    Decide which profession* you want to be, and choose. Or choose both. They both work.

    -------------------------------
    *I've been told that engineers make more money, but I know an engineer that just had his job outsourced to India. Quite dynamic times we live in.
     
    Last edited by a moderator: May 6, 2017
  14. Jul 28, 2012 #13

    I like Serena

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    Welcome to PF, bbgirl! :smile:

    The use of the words anode and cathode is always a bit ambiguous I'm afraid.
    I like to avoid them and just talk for instance about the positive terminal of a battery.

    Furthermore, you also have to make the distinction in which direction the electrons flow and in which (opposite) direction the current flows.
    In the picture you refer to, the arrows indicate the electron flow (instead of the current flow).


    From wikipedia: "In all electrochemical devices negatively charged anions move towards the anode (hence the name)."

    And: "In a discharging battery the anode is the negative terminal".

    And: "In a recharging battery, the anode is the positive terminal".


    The point is that inside your battery the electrons move toward the anode, making it the negative terminal.
     
  15. Jul 28, 2012 #14
    The following link applies the right-hand rule to conventional current.
    http://en.wikipedia.org/wiki/Right-hand_rule
    “This version of the rule is used in two complementary applications of Ampère's circuital law:
    An electric current passes through a solenoid, resulting in a magnetic field. When you wrap your right hand around the solenoid with your fingers in the direction of the conventional current, your thumb points in the direction of the magnetic north pole.
    An electric current passes through a straight wire. Here, the thumb points in the direction of the conventional current (from positive to negative), and the fingers point in the direction of the magnetic lines of flux.”

    Notice that the above rule is a “right hand rule” only for conventional current. For electron current, one has to use the corresponding “left hand rule”.

    I don't know if the book is still published. However, one book that addresses many of these issues is:
    "The Teaching of Physics" by J. W. Warren (Butterworths 1965).
    I bought a used copy of this book 10 years ago. I think it is wonderful. It is too bad that this book didn't become required reading for all physics and chemistry teachers. I wonder if there is a similar book that was published later.
     
  16. Jul 29, 2012 #15
    TY Darwin. I have referred to that wiki page often for the Right Hand Rule. I would love to get that book you recommend. Does it have a good simple battery diagram that also labels the anode & cathode.

    I can't imagine that we don't have a simple go-to well-labeled diagram for a battery somewhere that we can all agree on. Anyone an artist?:wink:
     
  17. Jul 30, 2012 #16
    Do you mean "The Teaching of Physics" by J. W. Warren (Butterworth, 1965)?
    Sadly, the book doesn't discuss electrolytic chemistry. The cathode versus anode problem is not discussed. It also doesn't discuss the the current conventions or hand rules. The book has a few illustrations, and a few equations. However, the emphasis of this book is apparently the use of words in physics.
    Sorry that I recommended that book with respect to hand rules. Hand rules are one of the topics that are best explained with pictures rather than words. Warren seems to avoid explaining things with pictures. He relies heavily on words. The issues that he addresses are those which are best addressed by a careful use of words.
    The book focuses on laws of physics that are commonly misunderstood with respect to words in sentences. Maybe the writer thought the cathode versus anode laws as part of chemistry rather than physics. Maybe there aren't many people who misunderstand "conventional current".
    The book focuses on topics that are considered basic physics rather than basic chemistry. For example, it goes into great deal on "electric potential" versus "EMF" and "Ohm's Law"
    The book seems to have its greatest strengths in issues that can't be explained clearly by a diagram. For example, diagrams don't really clear up issues concerning units. The book discusses CGS units. As another example, a diagram doesn't really explain "entropy".
    There is an important part of science that concerns the precise use of words. Many of the misunderstandings in science studies come from synonyms, antonyms, units, and grammar. I myself have worked very hard to learn how to explain things in words. I like this author because he addresses many of these word issues.
    Not every confusion can be explained by picture or equation. Pictures have a tendency to be ambiguous. So explaining an ambiguous word with an equally ambiguous picture is absurd.
     
    Last edited: Jul 30, 2012
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