Author Topic: On the topic of batteries and electrons/protons  (Read 5890 times)

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Offline ENIAC

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On the topic of batteries and electrons/protons
« on: January 12, 2015, 06:42:10 pm »
Electricity is the movement of electrons through a conductor from one atom to the next. My confusion is when we talk about electricity I often hear people say for instance a battery's power flows from the positive terminal to the negative terminal, in loop/circuit. Even though electrons are negative so don't they move from negative electons black gnd wire to positive protons red wire? I know a battery is just a chemical factory with chemical reactions going on that produce electrical energy. Does the chemical reaction cause the electrons/black gnd wires to flow the electrons from the negative terminal into the circuits of a car and then into the positive/protons to repeat the cycle?  :wtf: I know I have something very wrong here and I am confused so much please share your knowledge!

Thanks!
 

Offline IanB

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Re: On the topic of batteries and electrons/protons
« Reply #1 on: January 12, 2015, 06:49:29 pm »
Protons are not actually involved with electricity, they are buried in the middle of atoms and do not move.

For practical purposes electricity is just about the flowing of electrons from one place towards another (that is why electricity and electron are similar words).

When current flows in wires, it is electrons flowing from negative towards positive.

However, for historical reasons there is a convention that electric current flows from positive to negative. This is just a sign convention and makes no difference to normal calculations. It is just the same as saying that "heat" flows from hot to cold, while "cold" flows from cold to hot. The outcome is the same either way.
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Offline ENIAC

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Re: On the topic of batteries and electrons/protons
« Reply #2 on: January 12, 2015, 06:57:18 pm »
When you say "current flows in wires, it is electrons flowing from negative towards positive." I don't understand what is positive? what is negative? where is the distinction being made if it's all just the movement of electrons. I think I am too wrapped up into the whole negative=electrons, positive=protons idea. If we use the idea of a car battery is what you are saying is that electrons flow in the wire from the negative terminal to the positive terminal in the circuit? Is that right?
 

Offline ENIAC

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Re: On the topic of batteries and electrons/protons
« Reply #3 on: January 12, 2015, 07:01:16 pm »
On second thought I think I understand now. Since both a ground negative terminal wire and positive terminal wire are both made of copper they are the same thing? and electrons both flow through both of them but one first and the other secondarily? But I couldn't say take off my negative terminal and positive terminal and switch them? One part of the battery is pushing the electrons out and the other is catching them from the other end completing the circuit?
 

Offline ruffy91

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Re: On the topic of batteries and electrons/protons
« Reply #4 on: January 12, 2015, 07:02:27 pm »
Yes. And electrons carry a negative charge. So it's negative charge flowing in negative direction --> positive current.
 

Offline Yago

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Re: On the topic of batteries and electrons/protons
« Reply #5 on: January 12, 2015, 07:31:35 pm »
Think of it as one has more electrons than the other.
So the negative terminal has more electrons than the positive, so when connected the electrons flow from neg to positive in an attempt to equal the levels of electrons.
Similar how water will flow from high to low levels.

Also, the expression of "potential difference" instead of "Voltage" helps clarify this.
 

Offline okashira

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Re: On the topic of batteries and electrons/protons
« Reply #6 on: January 12, 2015, 07:35:47 pm »
 

Offline ENIAC

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Re: On the topic of batteries and electrons/protons
« Reply #7 on: January 12, 2015, 07:37:16 pm »
Then the way a lot of people talk about it being from the positive terminals to the negative terminal or "conventional current" is in fact wrong? because they were just guessing back in the beginning? In actuality "electron current" flow path goes from the negative terminal to the positive terminal. And therefore it's the other way around?
 

Offline Yago

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Re: On the topic of batteries and electrons/protons
« Reply #8 on: January 12, 2015, 08:00:19 pm »
Then the way a lot of people talk about it being from the positive terminals to the negative terminal or "conventional current" is in fact wrong? because they were just guessing back in the beginning? In actuality "electron current" flow path goes from the negative terminal to the positive terminal. And therefore it's the other way around?

Isn't either way round a matter of convention?
Negative and positive are just names that have been given.

Then there's the flow rate of about 5MPH or whatever it is, it is actually a "vibration" that cascades from one electron to another, akin to a Newtons cradle. (note, that's what I thought was going on, someone might come along and shout at me for being incorrect!)
 

Offline katzohki

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Re: On the topic of batteries and electrons/protons
« Reply #9 on: January 12, 2015, 08:04:45 pm »
Yeah, it's confusing. When we talk about Current (Amperes) it flows from positive to negative generally (conventionally). When we talk about electron flow, they actually go the other way. Like Voltage though, it's really just a reference frame and so you could define it the opposite and have "negative" current flow.

I guess the best thing to do is to go with the convention and sort of ignore electron flow. You generally don't need to think about electrons unless you're working on understanding silicon PN junctions or some such thing. Well it's one of those things that once you understand it you've made a good step forward in your electronics knowledge.

Oh yeah, and then there's "holes" ...

@Yago: yeah, that's called electron migration. More like vibration, true.
 

Offline IanB

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Re: On the topic of batteries and electrons/protons
« Reply #10 on: January 12, 2015, 08:34:11 pm »
One part of the battery is pushing the electrons out and the other is catching them from the other end completing the circuit?

Exactly this.

Furthermore, when the positive end of the battery catches the electrons it pumps them through the battery back towards the negative terminal so they can go round again. It is a chemical reaction inside the battery that does this pumping.

Also, take note of what Yago said, that the electrons don't actually move very fast inside wires. There is a huge number of electrons moving very slowly like a deep, slow moving river.
« Last Edit: January 12, 2015, 10:28:16 pm by IanB »
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Offline Yago

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Re: On the topic of batteries and electrons/protons
« Reply #11 on: January 12, 2015, 10:16:19 pm »
Does that mean I got promoted to a "somebody" now Ian? ;)
 

Offline IanB

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Re: On the topic of batteries and electrons/protons
« Reply #12 on: January 12, 2015, 10:27:52 pm »
Does that mean I got promoted to a "somebody" now Ian? ;)

Well there were several earlier posts and I couldn't remember who said what. Fixed now.
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Offline T3sl4co1l

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Re: On the topic of batteries and electrons/protons
« Reply #13 on: January 12, 2015, 10:34:16 pm »
Yes, the xkcd cartoon is basically our problem (for physicists and EEs, and to a lesser extent chemists and others).

If you open your mind a little and forget that just electrons are negative, you can run through the equations and find that everything works out perfectly fine with all signs reversed.  Which is as it should be.  You'll also be prepared for those situations when positive charge carriers are in fact physical, such as ionic conduction (in plasmas, ionic solutions and solids), hole conduction (semiconductors) and antiparticles (physics).

I've always wanted to build a proton vacuum tube triode.  Which should be possible, using a very weak hydrogen fill and a hollow cathode to produce the protons.  The device should have exactly the same characteristics as a normal triode, with signs reversed (so the grid becomes positive relative to the "cathode" to cut it off, and the plate is negative), and with uselessly low transconductance and propagation delay (about 2000 times worse, oddly enough). :)

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Offline retrolefty

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Re: On the topic of batteries and electrons/protons
« Reply #14 on: January 12, 2015, 10:58:51 pm »
Then the way a lot of people talk about it being from the positive terminals to the negative terminal or "conventional current" is in fact wrong? because they were just guessing back in the beginning? In actuality "electron current" flow path goes from the negative terminal to the positive terminal. And therefore it's the other way around?
Isn't either way round a matter of convention?
Negative and positive are just names that have been given.

 But not equal conventions as the "conventional folks" got to define the arrow direction on all semiconductor symbols.  ;)
 

Offline Yago

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Re: On the topic of batteries and electrons/protons
« Reply #15 on: January 12, 2015, 11:07:25 pm »
Does that mean I got promoted to a "somebody" now Ian? ;)

Well there were several earlier posts and I couldn't remember who said what. Fixed now.

Ah, I was only having a laugh!
No worries bud :)
 

Offline amyk

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Re: On the topic of batteries and electrons/protons
« Reply #16 on: January 12, 2015, 11:46:03 pm »
One part of the battery is pushing the electrons out and the other is catching them from the other end completing the circuit?

Exactly this.

Furthermore, when the positive end of the battery catches the electrons it pumps them through the battery back towards the negative terminal so they can go round again. It is a chemical reaction inside the battery that does this pumping.

Also, take note of what Yago said, that the electrons don't actually move very fast inside wires. There is a huge number of electrons moving very slowly like a deep, slow moving river.
That reminds me of this exam question:

Quote
Which of the following best describes the process that occurs when a battery is being (electrically) charged?

A. Electrons enter its positive terminal
B. Electrons enter its negative terminal
C. Electrons enter its positive terminal and exit its negative terminal
D. Protons enter its positive terminal and electrons enter its negative terminal
E. Electrons enter its negative terminal and exit its positive terminal
F. None of the above

I don't remember the exact statistics, just that this was given to students in a highschool physics class and the majority of them got it wrong.
 

Offline KM4FER

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Re: On the topic of batteries and electrons/protons
« Reply #17 on: January 13, 2015, 12:08:41 am »
OK, I'll bite......

Obviously F is the best answer since all the others are equally true.

earl...
 

Offline T3sl4co1l

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Re: On the topic of batteries and electrons/protons
« Reply #18 on: January 13, 2015, 12:34:13 am »
E is correct, since (unless the terminals are made of ionic conductors such as I gave examples of), protons (or any other ions) aren't moving at all, and electrons are entering and exiting at the same time (conservation of charge).  Any other answer causes the battery itself to develop a massive voltage with respect to its surroundings, which doesn't make a damn bit of sense (an electrostatic charge can be seen as electrons entering (or exiting) and nothing else; for everything else, see Kirchoff).

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Offline IanB

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Re: On the topic of batteries and electrons/protons
« Reply #19 on: January 13, 2015, 01:01:01 am »
I think E represents a battery being charged (the question asked), while C represents a battery being discharged (a valid process, but not what was asked about).
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Offline T3sl4co1l

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Re: On the topic of batteries and electrons/protons
« Reply #20 on: January 13, 2015, 01:54:04 am »
I think E represents a battery being charged (the question asked), while C represents a battery being discharged (a valid process, but not what was asked about).

:nod:

(I note we still don't have a :nod: emote.. :( just imagine that we do)

Tim
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Offline ENIAC

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Re: On the topic of batteries and electrons/protons
« Reply #21 on: January 13, 2015, 02:04:38 am »
Alright I think I may be understanding, in terms of a car battery. When the chemical reaction takes place in a battery after a car has started the electrons in the negative terminal side of the battery have more electrons and since electrons are attracted to wherever there is less electrons (positive end of the battery) this creates the voltage or pressure to get them to move in the copper wire?

What creates this displacement of electrons. Like when you start a car why does one end automatically have more electrons thus forcing exchange.
« Last Edit: January 13, 2015, 02:06:12 am by ENIAC »
 

Offline IanB

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Re: On the topic of batteries and electrons/protons
« Reply #22 on: January 13, 2015, 02:17:19 am »
If a battery is just sitting there by itself then chemical reactions* inside the battery cause a buildup of electrons at the negative terminal and a lack of electrons at the positive terminal. This displacement of electrons causes an electrical pressure to exist (measured as voltage) between the terminals. As soon as you connect a bulb, a motor, or even just a wire between the terminals this provides a pathway for the electrical pressure to be released and current flows through the circuit from high pressure to low pressure.

Note that the pressure is always there, which is why batteries have a voltage even when nothing is connected. When you connect a load, then current flows, and a circuit is created.

When a car battery is being charged, the electrical generator inside the car (the alternator/rectifier/voltage regulator system) generates a voltage higher than the battery voltage and thus is able to force electrons "the wrong way" through the battery, reversing the chemical reactions and adding charge back into the battery.

* Note that the chemical reactions are strictly speaking described as electrochemical reactions, but this is only a matter of terminology and it doesn't change what is going on.
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Offline Syntax_Error

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Re: On the topic of batteries and electrons/protons
« Reply #23 on: January 13, 2015, 02:43:42 am »
Don't slap me too hard Ian, as I know this is your area of expertise:

I'd like to add that in a chemical battery, the open circuit voltage developed at the terminals is directly determined by the reaction potentials of the two half cells used to make a battery cell, and the sum of all such cells connected in series. So, in a car battery, the lead acid half cells develop a little over two volts potential per cell, and six cells are connected in series to get your "about 12 volts" in the battery.

Lastly, it is this electrical pressure that causes the reaction to cease. Why doesn't the reaction proceed until the chemicals are used up and make a billion volts? The reaction is halted when the electromotive force is equal to that of the cell voltage. When you connect a load or a wire between the terminals, the potential difference drives charge from one terminal to the other, and this reduces the voltage on the terminals, which in turn allows the chemical reaction to proceed forward, generating more charges and maintaining the voltage (mostly). Remove the connection between the terminals, and the reaction will produce charges until the terminal voltage is high enough to halt the reaction, and the process stops.
It's perfectly acceptable to not know something in the short term. To continue to not know over the long term is just laziness.
 

Offline T3sl4co1l

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Re: On the topic of batteries and electrons/protons
« Reply #24 on: January 13, 2015, 05:39:47 am »
Although a related question is also,

If it should happen (thermodynamically speaking), why doesn't it?

Meaning: clearly, a battery should self-discharge, but the rate is the important factor here.  How fast does it react, with or without an external load, and why?

If you put aluminum foil in strong base (NaOH / KOH in H2O), no matter how much voltage you superimpose between the two, it reacts spontaneously.  This is a kinetically favorable reaction.  The reaction does develop voltage all its own, but not nearly as much as you would hope, and it can't be retarded or even reversed by applied voltage alone.

The nice thing about zinc under similar conditions (which is what's used in alkaline cells, but similar reasons follow for all types), is the reaction kinetics are low: it tends not to proceed, just sitting there; but it develops a voltage, and when you short that out, it's enough to overcome the kinetic barrier and the reaction proceeds.  Presumably, that should suggest that all cells which don't rapidly self-discharge should necessarily experience a terminal voltage drop in use; and the amount of drop is proportional to rate (effectively: how much voltage drop you're "paying" to "bribe" the kinetics into moving) and self-discharge (which might simply be seen as a Norton current source, where the self-discharge current is as large as the load current).  This is certainly apparent for several main types (alkaline, NiMH, etc.), but... doesn't seem to follow for others (Li ion, poly?).  Differences in chemistry probably dominate as always, or this could simply be an incorrect analysis.

Tim
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