Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I need halp

  1. Apr 5, 2005 #1
    i know thats electricity usually have two cables one for the plus charge and one for the minus charge but i know the minus charge is a fluid of electrons so what about the plus charge ??????
     
  2. jcsd
  3. Apr 5, 2005 #2

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    I'm sure you got them all mixed up...Let's leave the sockets out and think what's going on in a metal (as opposed to other electrically conductable media).

    The free electrons move around (thermal movement).Assume that u apply a(n) (electric) potential difference at the ends of the metal conductor/wire.That means that at one end (call it A) the electric potential is higher than it is at the other end (call it B).

    Mathematically [tex] \phi_{A}>\phi_{B} [/tex]

    A difference (fancy terms:gradient) of potential induces a nonzero electric field.

    [tex] \vec{E}=-\nabla\phi [/tex]

    This field definitely has an orientation.It can be determined.It points towards (in vector language,the top of the arrow) the end with a lower potential.So it points from A to B. How will the charged particles (electrons,in this case) move...?They have to move,because they're acted on by a force,the electric force

    [tex]\vec{F}=q\vec{E} [/tex]

    They'll move from B to A.How do i know that?The acceleration vector points from B to A.How do i know that?well,the acceleration has the same sense with the force (mass is constant and positive).The force has the same orientation as the product (electron's electric charge times electric field).The electric field points from A to B,but the electron's electric charge is negtive ([itex] q_{el}=-e\approx -1.6\cdot 10^{-19}C [/itex]).

    So that's the whole story.The simple picture behind electric current in metals...In metals,there are no moving "+" charges (in electrolytes,plasma and semiconductors this is no longer valid)...

    So that's the sense of the electronic (i.e. caused by electrons) current.Always fom smaller potential to larger one...The weird part is that in diagrams (in physics books,and engineering ones,too),the arrow that u put when writing "I" doesn't show the real sense of the electronic current.It's the opposite of that.


    Daniel.
     
  4. Apr 5, 2005 #3
    i think your question can be answered more simply than dex wrote out. First, the stuff flowing through wires is always electrons. The reasons some wires are hooked up to positive or negative terminals is because of the way the electrons are flowing.

    Think of a simple circuit: a battery hooked up to a lightbulb. You have one wire connected from the positive terminal of the battery to the lightbulb. This is your "positive cable." Then you finish the circuit by hooking the lightbulb back up to the negative terminal using another wire, your "negative cable." The electrons leave the negative terminal and try and get to the positive terminal, (electrons are negative, so they're attracted to positive.) This causes a current in the opposite direction, since electrons carry a negative charge. Really, there are no "positive or negative cables," we just have to connect things so that our electrons can flow, and this requires that we know which way the current is going through our wires so that everything goes from positive to negative.

    i hope that helps....
     
  5. Apr 5, 2005 #4

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    Here's something that you ought to read...

    Gale,i hope your test is on electricity... :uhh: If it isn't,get your u know what back to work !! :grumpy:

    Daniel.
     

    Attached Files:

  6. Apr 5, 2005 #5

    Integral

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Dexter,
    I find such articles nearly offensive. They assume that someone knowledgeable enough to understand electron flow in electronic circuits is to stupid to understand ionic current in chemical solutions.
    I do not understand what that post has to do with the current topic other then further the confusion.

    Can we simply say that in the case of electronic circuits electron flow is the dominate mode and not worry about electrolytic solutions.
     
  7. Apr 5, 2005 #6

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    I agree,Integral.I didn't post it as in insult to anyone,as i'm sure it hasn't been written/conceived as an insult.People have misconceptions and those tend to propagate a lot easier that the correct information.We have to do something about it,though.

    Maybe the style wasn't pretty,but what matters is that it was scientificaly correct and didn't use mathematics.It was like old fashioned phyisics...

    Explaining concepts and correcting misconceptions are the most difficult things in a teacher's life...

    So i think it can still be useful to anyone,that's why i posted it.If u think otherwise,u can remove it.

    Daniel.
     
  8. Apr 5, 2005 #7

    Gokul43201

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Besides, the "+" and "-" on the terminals of a power plug or cable DO NOT represent the sign of the charge. They represent the sign of the voltage (potential) applied at that terminal.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: I need halp
  1. I need help (Replies: 13)

  2. I really need help (Replies: 9)

Loading...