Confusion about the "+ v -" notation

Discussion in 'General Electronics Chat' started by Ulfalizer, Jan 16, 2009.

  1. Ulfalizer

    Thread Starter New Member

    Jun 29, 2005
    5
    0
    Hi,

    How exactly does the "+ v -" notation for specifying the voltage across a component (e.g. a resistor) work? Is the + side always oriented towards the + side of the voltage source, so that it's just a mnemonic for remembering what direction current goes in, or is there some deeper meaning? Will exchanging + and - result in a nonsensical schematic?

    /Ulf
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Machs nichts across a resistor, but polarity becomes very significant relative to a sensitive component like a transistor, diode or polarized capacitor.
     
  3. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    For batteries and power sources the positive side is the side where the current goes out of the battery or power source. For resistors and other components (active or passive) the positive side will be on the side where the current enters the component. Take care of capacitors and inductors because sometimes they act like sources and sometimes like passive components.
     
    Last edited: Jan 16, 2009
  4. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
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    The "+" corresponds to the point of higher potential; whereas the "-" corresponds to the point of lower potential - with respect to the component.

    Dave
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    And for us grunt techs potential is another word for voltage. :D Engineers :rolleyes:
     
  6. italo

    New Member

    Nov 20, 2005
    205
    1
    A [+] does not signify a higher-lower anything but is does imply a current flow direction mainly electrons as opposed to holes.
     
  7. Ulfalizer

    Thread Starter New Member

    Jun 29, 2005
    5
    0
    I think you've cleared it up for me. Thanks!

    /Ulf
     
  8. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
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    Which is a function of the potential and is a notation dependant on whether current is defined in terms of conventional or electron flow. Defining it in terms of flow direction of electrons and holes is nonsensical in the case of many passive devices. Remember the OP is asking about the + and - notation for voltage specification across a component; I think you are think about the + or - notation sometimes applied to certain active devices.

    IMO it is a clumsy notion, but some (still) use it.

    Dave
     
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