current direction

Discussion in 'Homework Help' started by Earless, Aug 23, 2007.

  1. Earless

    Thread Starter Member

    Aug 23, 2007
    Im currently in EE 101 and dont quit understand the direction current arrows.How can an arrow pointing in two diections be equal, The book says a current is either moving w/ 3 amps to the right or -3 amps to the left, and that they are both equal?wtf???
  2. nanovate

    Distinguished Member

    May 7, 2007
    Their magnitudes are equal.
  3. Dave

    Retired Moderator

    Nov 17, 2003
    The direction is defined by the + or - sign, + being one way and - being the opposite (180deg). As nanovate says, the magnitudes are the same because the net current flux through a cross-section is the same size in either direction - the only difference is the direction defined by the sign. I suppose an analogy with classical physics would be Newton's Third Law where each action (in this case positive current flow) has an equal and opposite reaction (in this case the negative current flow).

  4. Earless

    Thread Starter Member

    Aug 23, 2007
    So current travels from left to right and right to left at the same time with the same magnitude,hence the triviality of direction?Is that what your saying?EE isnt my best subject but thats F'in thinking of current as a physical flow that has a definite and unique direction,like a river.Theres is a problem in my book [​IMG]
    why are the answer what they are???how do you know which is plus and which is minus?
  5. star


    Dec 18, 2006
    For conventional current: +ve is current travelling from the positive electrode of the voltage source to the negative electrode. If you have a current source, then +ve is in the direction indicated by the current source.

    I don't think dave means that current travels from right to left and left to right simultaneously. Current (conventional current) in reality only travels in one direction, in the direction as explained above. The arrows put there are arbitrary, decided by whoever who drew them, perhaps to simplify a problem they're working on. So say if the arrow is pointing in the direction that the current (conventional current, not electrons) actually flows in real life, then the direction is positive. However, if the arrow is pointing in the other direction, then it is marked as -ve.

    i'm guessing if that's all there is to the diagram, then you can't really tell, and as long as one is the negative of the other, it should be fine.

    I hope that helps.
  6. recca02

    Senior Member

    Apr 2, 2007
    the direction of current by convention is from higher potential to lower potential.

    an alternating current has no fixed direction.

    and while analysing a circuit if u get stuck on deciding the direction of current in a loop/component choose any arbitrary direction and a arbitrary variable to represent its magnitude. u'll always get a correct answer irrespective of the direction u chose (but it depends if u solve it correctly or not). if u get a negative in front of magnitude it means the current is in opposite direction to the arbitrarily chosen direction. not only this u can keep the chosen direction unchanged(but keep the sign intact) and solve for any other unknown quantity in the circuit and ..amazing u still get a correct answer!!!
  7. Distort10n

    Active Member

    Dec 25, 2006
    Recca02 brings up a good point. When doing circuit analysis, you can pick the direction and magnitude of the current. The only caveat is that you must remain consistant with that direction and magnitude throughout the circuit for the final answer to be correct.
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