Why do cables and batteries have a positive and a negative side?

Question

I am a beginner in electronics, mostly self-taught. If electrons are negatively charged and are the reason for electric current why is there a 'positive' side on a battery and negative one? Don't electrons just flow out of one of those two sides? To my knowledge only one side pushes electrons and the other does nothing, how exactly does this work?

What is a 'ground' anyways? I have read that the negative side is the ground and yet it is the side that pushes electrons in a battery, is that correct?

Answer 1

Electrons flow out one side (the negative one) and come back in from the other (the positive one). Current is not associated with electron accumulation, but with electron flow. The point of the battery is pushing electrons from the positive to the negative terminal: this pushing requires energy, that is chemically kept in the battery, used to push the electrons that then release it when they go through your circuit.

The negative sight might be or not ground. Ground is a word that is used to refer to a circuit particular node, sometimes connected to ground. You measure all voltages with respect to this node, so it is the zero voltage node. I understand you might think that electrons might escape if ground is connected to the negative terminal of the battery but that is not possible since they must go back in the battery because no net charge accumulation is allowed. If an electron pushed by the battery happens to escape through ground, another one will come from ground, make it through your circuit and then back in the battery.

Answer 2

If electrons make one side of the battery negative, then the other side is lacking those electrons and wants them. Because the positive terminal is lacking those electrons it has a much more positive voltage. It likely has a lot more protons (which are positive) than the negative side of the battery. Electrons flow from low potential to high, so they want to push away from other electrons as much as they want to be pulled by positive charges (protons or 'holes' in semiconductor devices).

Ground has multiple meanings. Most often it just means where you want your reference voltage to be. Usually as a reference voltage, you just set it to 0 V because it's easy to work with. Once you have a reference voltage, you can state that all other voltages in a circuit are some finite distance away from Gnd. You could arbitrarily state that the positive terminal is the ground though and then your negative terminal of a battery would give you a negative voltage. They're both completely valid points of view. Or maybe in Einstein's words it's 'relative'.

Answer 3

You are partly correct. Electrons are "pushed" out from the negative terminal to travel to the more positive terminal. They can't travel to a more negative terminal (if there were one) because that "more negative" terminal would be pushing electrons at it.

Conventional current ought to be the direction of the flow of electrons but it isn't and as EEs you learn this early on and just accept that mistakes were made sometime in the 1800s. So conventional current flows from positive terminal to negative terminal and, electron flow is the reverse.

A higher flow of electrons occurs when the positive terminal becomes more positive (compare a 1.5 volt battery with a 9 volt battery - for a given load resistance, more current flows. You can connect many batteries in parallel and without the terminals bearing a name you might wire them the wrong way round and cause a fire - in effect this would be two batteries in series shorted out (if you think about it).

Ground aka earth aka 0V aka chassis can be any voltage positive or negative - it's just a reference point that is used to measure voltages against.

Answer 4

If electrons are negatively charged and are the reason for electric current

Electrons do carry negative electric charge but electrons are not the reason for electric current. It is true that a flow of electrons is an electric current but the reason for the flow of electrons is not electrons themselves or that electrons are negatively charged, it is that, loosely speaking, one side of the battery is pushing and the other side is pulling electrons.

Don't electrons just flow out of one of those two sides?

Yes, and they flow in to the other of those two sides.

To my knowledge only one side pushes electrons and the other does nothing, how exactly does this work?

The other side attracts (pulls) electrons.

What is a 'ground' anyways?

In this context, it's simply what we choose to reference all of our voltage measurements from. In other words, it's the place to put the black lead of your voltmeter. There's more to it than that but, at the level you're at now, this is close enough.

Answer 5

See Automotive electrical system. How does everything work?

In some ways, the important thing is the electrical field transmitted through the wiring that causes current to flow. Using the water pressure analogy, if you have a series of pipes and apply pressure to the end of one, pressure will be transmitted everywhere in the pipe system even if the water isn't flowing.

Answer 6

The following is a really simplified view of things but I hope it helps.

Let's say you take a battery and connect it to a resistor. The resistor would have a zero charge. Electrons from the negative pole will want to jump to the resistor, until the charge density on the resistor and battery are similar. If the other end of the resistor is connected to the positive pole of the battery, the extra electrons will want to travel from the resistor to the positive pole of the battery following the charge density gradient. Now the chemical process within the battery is "triggered" and these electrons are again "moved" to the negative pole of the battery. So, now you have a circuit the electrons go around. So electrons do flow out of the negative side. The positive sign indicates this side is positively charged compared to the negative side. This is due to electrons moving from the positive to negative side and from positively charged ions moving from the negative to the positive side.

The "ground" refers to a point of your circuit, arbitrarily chosen to be the circuit's 0V voltage reference. If the circuit is actually connected to the earth, then that part will become equipotential to the surface of the earth. If the circuit is not physically connected to the earth, then the circuit is called "floating".