conventional flow query

Discussion in 'Feedback and Suggestions' started by Winston, Dec 25, 2007.

  1. Winston

    Thread Starter Member

    Dec 25, 2007
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    0
    Hello. I read, I think, the bit about conventional flow and electron flow. It describes the diagram of conventional flow as the plus representing a surplus of e's, so charge is flowing from there to the negative side, the deficient side. But then it goes on to say that this is technically incorrect, and that the electron flow diagram is correct because it shows the actual flow of electrons. Isn't it the case that both are correct as far as direction of e's but that the conventional has a plus where all the e's are at and the electron flow diag. has a minus where the all the e's are at? Many thanks. Excellent site. I recommend it a lot.
     
  2. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    144
    Hi Winston,

    Thank you for the comments. I assume you are talking about this section: http://www.allaboutcircuits.com/vol_1/chpt_1/7.html

    The above section is correct in its assessment of conventional and electron current flow. We need to be clear that when we are talking about current flow we are talking about the movement/migration of mobile electric charge within a conductor typically under the influence of an applied voltage. Electrons are both negatively charged and mobile, and hence will flow from negative to positive and not the other way. The positive charge is attributed to protons which are immobile (not mobile) and hence do not move under the influence of a voltage in the way electrons do.

    The ideas of conventional and electron current flow are equally applicable for the purposes of analysing electronic circuits, where a change of sign will denote the changes in current flow type. This is intuitive due to considerations of conservation of energy.

    Has that cleared any ambiguities up? If not, post back and I'll try and explain further/clearer.

    Dave
     
  3. Winston

    Thread Starter Member

    Dec 25, 2007
    22
    0
    I know. But the section says that the conventional diagram is "technically incorrect". I'm wondering in what way. It states that the plus is representing a surplus of electrons. So the arrows are pointing in the right direction for e flow. I can only guess that "technically incorrect" refers to the fact that we don't call electrons "positive".

    My position is that we should dispense with calling them negative and positive, call a surplus of any charge plus and a shortage negative and in the special case where protons are flowing just make a note.

    Exactly. It doesn't matter. It seems clutzy to the point of silly to give the two charges extra names, names that don't even make any sense. Just call them protons and electrons and call a surplus "+"...

    The fun is in sorting it out. Well, finally sorting it out, too.
     
  4. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    144
    In essence you are correct when you say that "technically incorrect" refers to the fact that electrons are negative and not positive. However the reason for this confusion stems from our forefathers who initially though that current flow was a flow of positive charge and therefore from positive to negative because, to quote the e-book: "we tend to associate the word "positive" with "surplus" and "negative" with "deficiency"

    After this concept of current flow became accepted, we discovered that in fact the opposite was actually and physically true; that is current flow is a movement of electrons which, in the model of the atom, are negatively charged. Therefore our forefathers got the notation back to front.

    Conventional current flow and electron current flow, as described in the above linked e-book section, are both accepted ways of describing current flow. In order to dispense with calling something positive and negative would require rewriting many texts on this subject in order to provide consistency. In fact it would create several issues; firstly, it would remove the tie between the accepted atomic model from which the fundamentals of current flow are assumed. Secondly, the positive and negative notation are particularly important in understanding and analysing electronics circuits - could you imagine performing one of the circuit analysis methods (branch current, KCL etc) without the idea of positive and negative directions? As long as you maintain consistency with the notation you use, then you are able to analytically understand most circuits.

    It is also worth noting that protons, positive charge, do not flow in the way electrons do. Protons are intrinsic components of the atomic nucleus and are therefore tied to nucleus - they will not flow in the presence of an applied voltage. In semiconductor theory, there is the concept of a "hole" which flows like electrons which has a positive charge - in fact the "hole" is nothing more than an absence of an electron.

    Indeed it does raise confusion; however this is the way that this topic is approached mainly due to the historic description of positive-negative conventional current flow and the actual negative-positive current flow. To not make our readers aware of this in the e-book would make it difficult for them to grasp the multi-treatment of current flow as discussed in almost all other texts on electronics.

    Indeed it is :)

    Dave
     
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