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I'm trying to understand voltage and there is a site that says that the battery do work to a positive charge to move it from the low potential terminal (negative) to the high potential terminal (it gains potential energy doing that):

"The battery simply supply the energy to do work upon the charge (positive charge) to move it from the negative terminal to the positive terminal. By providing energy to the charge, the cell is capable of maintaining an electric potential difference across the two ends of the external circuit."

(from the beginning of the fifth paragraph from this site : http://www.physicsclassroom.com/class/circuits/Lesson-1/Electric-Potential-Difference )

Maybe my question is silly but it says that the battery do work on the positive charge to move it from the negative to positive side, but my understanding of a battery is that it creates an electric field and the positive charge in the high potential terminal is full of potential energy and the charge naturally move from the positive side to the negative side (to lose potential energy like for gravity), but the text says it's the other way around.

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  • $\begingroup$ I don't know whether this applies to your problem, but all this +/- business on batteries/electic fields is a mess, with physicists using a different convention than engineers, etc. Basically what is + for a physicist is - for an engineer. $\endgroup$ – user1583209 Dec 16 '16 at 21:03
  • $\begingroup$ Yes, I do have troubles with +/- but in this text they clearly go with positive charge and they say that it goes the opposite direction of what a positive charge would go according to the convention. (At least to my knowledge) $\endgroup$ – gigi Dec 16 '16 at 21:11
  • $\begingroup$ Related question by OP: physics.stackexchange.com/q/299141/2451 $\endgroup$ – Qmechanic Dec 16 '16 at 21:39
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You and the part of the text you mention ("The battery simply supply the energy to do work upon the positive charge to move it from the negative terminal to the positive terminal") are talking about different part of the circuit.

Your are talking about the external circuit: the positive charges have high potential energy at the + (where + stands for high potential). When the circuit is closed, the electric field provided by the battery (or the potential difference, as this is just another way of talking about electric fields) pushes the positive charges to the - (low electric potential).

The text, however is talking about what happens inside the battery. Chemical processes 'push' positive charges from - to +, thus giving them back the potential energy they lost in going from + to - in the external circuit.

You can compare it with a ski lift: on the ski piste, the skiers go downhill. The lift, however provides the work to push them up the hill again so they can ski down again.

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  • $\begingroup$ Thank you so much. But is that what really happens in the battery? Do the same electrons that arrive in the positive terminal return to the negative terminal passing by the electrolye? $\endgroup$ – gigi Dec 16 '16 at 21:54
  • $\begingroup$ In short, chemical potential energy (which of course is electric in nature) is converted to electric potential energy (in the larger scale of the circuit). I would recommend to read this part of wiki on batteries. The same electrons are not passing by the electrolyte, as they are used to reduce the cations $\endgroup$ – Dries Dec 16 '16 at 22:06
  • $\begingroup$ There's no way to tell if the 'same electrons' do anything due to their indistinguishable nature. This goes way beyond the scope of this question though, as it's a delve into the quantum mechanical properties of the electron - but I thought it was worth noting for completeness. $\endgroup$ – codeAndStuff Dec 19 '16 at 17:56
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The convention of positive charges moving was introduced before we actually found out that the positive charges were in the nuclei, which are fixed in the lattice of the conductive material. The negatively charged electrons are actually what are moving.

Just remember like-charges repel one another, as nature tends toward lower potential energy states, so negative charges flow from the negative terminal toward the positive terminal. Or in the classical convention (moving positive charges), the positive charge flows from the positive terminal to the negative terminal.

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