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In other words, why do we need to connect the battery positive to the negative to get electron flow? As far as I know, voltage difference is what drives current flow.

From what I understand, there's a surplus of negative charge (electrons) in the positive end of a battery (weird I know, but I guess they do it for mathematical reasons). Between the positive and negative ends of the battery is some kind of wall that prevents the electrons from diffusing, so they have to go the long way (through a wire to the other end of the battery) to diffuse and reach the receiver atoms/molecules.

So why not just have the surplus of electrons on one end go to ground to equalize (e.g. 5 volts to 0 volts should produce current)? Why does it have to be the other end of the battery? I'm sure there's atoms/molecules in the ground that could accept the extra electrons (receivers atoms/molecules for the donors in the battery).

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    \$\begingroup\$ There's a tiny deficit of electrons on the battery's positive side, but once that equalizes (very quickly) there's now a tiny surplus of electrons on the battery's negative side. Or in other words the positive side is now at 0 volts and the negative side is now at -5 volts and no current is flowing. \$\endgroup\$ – immibis Nov 9 '17 at 3:02
  • \$\begingroup\$ I dont think this question will get answered to the satisfaction of OP unless someone is willing to dedicate a fair amount of time to writing a pretty long explanation. Maybe theres a satisfying explanation on the internet that someone can link to? \$\endgroup\$ – BeB00 Nov 9 '17 at 3:35
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    \$\begingroup\$ Connecting just one terminal to 'ground' can't cause a continuous current because current into / out of just one battery terminal would cause the battery to become electrically charged quickly putting a stop to the current. \$\endgroup\$ – Alfred Centauri Nov 9 '17 at 3:58
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    \$\begingroup\$ "ground" has absolutely no relevance to a battery until you connect it to one terminal, in which case it follows that you had better not also connect it to the other. \$\endgroup\$ – Chris Stratton Nov 9 '17 at 6:03
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Consider two atoms sitting beside one another. Each atom is normally balanced with an equal number of protons and electrons. As you know, protons have a positive charge and electrons have a negative charge. Everything is balanced.

If an electron is persuaded to move from one atom to the other, the second atom will now have a negative charge and the first, now an ion, will have a positive charge. This is now unbalanced. Nature does not like imbalances. The electron will, if not hindered, immediately return back to the positively charged ion. (Actually its a bit more complicated than that, and electrons tend to swish around a bit, but the net charge effect is the same.)

In a battery, a chemical reaction takes place which makes the electrons leave the positive terminal, leaving ions, and gather on the negative terminal. This makes a potential difference across the terminals. When sufficient voltage difference builds up between the electrodes, electrons can no longer make the journey across the battery and the chemical reaction suspends.

You now have something that is imbalanced.

If you hook a wire between the negative and the positive terminals, the electrons from the negative terminal and the electrons in the wire move around to restore that balance. As they arrive at the positive terminal, they reunite with ions, that allows the chemical reaction to advance, which creates more free electrons, and the battery continues to operate till the reaction is exhausted.

So, to recap, current flows around that circuit to balance the difference in charges in atoms in the circuit. However, as an entire entity, that battery circuit has a neutral charge. Even though the charges are not balanced within it, the total number of positive ions and negative electrons is still equal.

When you connect the negative terminal to earth the electrons do not cross over to ground. Why? Because they have no reason to. Because the battery, as a whole, is still charge balanced, there is no motive force to cause an electron to move. There IS NO surplus of electrons on the battery. Moreover, if some wayward, rebellious, electron were to try to venture across to ground, the battery would now have a net positive charge, and the electron would be pulled back in, or immediately replaced with another one from ground. Either way, no net current can flow to ground.

Ultimately, it's the same as the two atoms we started out with but on a macro scale, where the battery is one atom and the planet is the other.

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    \$\begingroup\$ Interesting, so the negative terminal is really the terminal that the electrons move from and not the positive terminal? And moreover, a battery cannot discharge current unless its circuit is completed since it stores energy in chemical form, which is different than a capacitor which stores energy more as a raw imbalance of electrons outside chemical reactions? And the battery is net neutral, so that's why electrons don't want to flow out of the battery unless they can make it to the other terminal of the same battery? So the battery is like one giant atom/molecule sort of (in terms of charge) \$\endgroup\$ – MechE Nov 9 '17 at 14:02
  • \$\begingroup\$ Also, electrons leaving the negative end would just create a greater potential difference with the positive end since there's even less electrons to balance it now in the battery, right? Even though the two ends are somehow separated, they can still "see" each other's potential difference through the electric field or something. \$\endgroup\$ – MechE Nov 9 '17 at 14:11
  • \$\begingroup\$ @MechE you got it... ;) And yes, electrons go the opposite direction from what we call current. Blame Benjamin Franklin and his predecessors for that one. Yes, electromagnetic fields need no conductor, they travel through space, including the space between atoms, so the electrons on the negative terminal feel the force from the positive terminal and remain there, held back by the electrolyte. Battery chemistry is a bit difficult to get your head around though, there are lots of articles on line, but the basics are as I have mentioned, so don't dwell on it. \$\endgroup\$ – Trevor_G Nov 9 '17 at 14:53
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It is 'potential' energy. Think of a car battery. The negative terminal of the battery is connected to the chassis of the car. So is every electrical device in the car. Everything is also directly or indirectly connected to the positive terminal of the battery. Everything 'sees' the potential difference between the positive and the negative terminals of the battery.

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