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Current flows from where and what charged particle does moves in a current ?

  1. Feb 28, 2015 #1
    Current moves from positive terminal to negative terminal. But electrons moves from the negative terminal to positive terminal due to its smaller mass . But why it is said that current moves from positive terminal to negative terminal ?
     
  2. jcsd
  3. Feb 28, 2015 #2

    Dale

    Staff: Mentor

    Electrons are negatively charged, so when an electron moves the current points in the opposite direction of its motion.
     
  4. Feb 28, 2015 #3
    could you explain it more briefly please. Thanks
     
  5. Feb 28, 2015 #4

    CWatters

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  6. Feb 28, 2015 #5

    Dale

    Staff: Mentor

    Current is about conservation of charge. We know that charge is conserved, so current is about telling us how this conserved thing changes. If the charge is increasing in some region, then by conservation of charge, there is a current flowing in to that region.

    Suppose that we have two spheres connected by a wire and electrically isolated from everything else. Now, if the right sphere becomes positively charged then by conservation of charge the left must become negatively charged. So, we want to DEFINE current as a flow of charge from the left to the right, to reflect that conservation of charge.

    Now, let's look at how the right sphere could become positively charged. You could have positive charge carriers move from left to right, so the current would be in the direction of motion. However, you could instead have negative charge carriers move from right to left. That would still accomplish the end point of having a positively charged sphere on the right and negatively charged sphere on the left, and in that scenario we have DEFINED our current to go from left to right, so the current is in the opposite direction of the motion the charge carriers.
     
    Last edited: Feb 28, 2015
  7. Mar 1, 2015 #6
    Motion of flow of current from positive to negetive terminaal is just a convention.what moves are actually the electrons from negetive to positive terminal and thus if you look at a very small part of a conductor motion of electrons in one direction can also be relatively thougt as motion of protons in opposite direction
     
  8. Mar 1, 2015 #7
    Way back when the laws of electricity were first being discovered it was thought that positive charges moved from positive to negative. The mathematics and rules developed on this idea produced correct predictions and allowed electronic devices to be designed. It became a standard way of thinking about how electricity behaves. Later, it was discovered that it was wrong. What really happens is that negative charges (electrons) move from negative to positive. By the time this was discovered however the previous positive-to-negative idea had become so universally accepted and used that people continued to use and and continue to use it to this day. Everybody knows that it is not a correct theory, but it's easy to use and produces correct prediction in almost all circumstances so it is still useful for figuring things out.
     
  9. Mar 1, 2015 #8
    An execellent elaboration of my thoughts.:-p
     
    Last edited: Mar 1, 2015
  10. Mar 2, 2015 #9

    Dale

    Staff: Mentor

    I wouldn't say that it is wrong. It is just a convention, and like all conventions, it could have gone the other way.

    There are cases, particularly in electrolytes, where the current is mainly due to the movement of positive charge carriers, and even more commonly cases where both positive and negative charge carriers play a role. Currents at electrodes often involve positive charge carriers in the electrolyte and negative charge carriers in the electrode, both moving towards or away from the electrode.
     
  11. Mar 2, 2015 #10
    Inside a conductor it is impossible for positive charged atoms to move.they are queit greater in size than an electron and thus have very less mobility.
     
  12. Mar 2, 2015 #11

    Dale

    Staff: Mentor

    Inside metal, yes, but not inside an electrolyte. In an electrolyte the positive and negative charge carriers are often similar mass and similarly mobile. Similarly, in a plasma the current consists of the motion of both positive and negative charge carriers, even though the positive charge carriers are more massive.

    Metals are not the only conductors.
     
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