Earth grounded, where does the current flow?

[lukka98]

TL;DR Summary

I have a few question about earth grounding that i don't understand.

My questione are these:
-If i have a voltare source (like a battery) that supplies a 5V voltage difference between its terminals, and there is a parth from positive to a resistor and then to ground, with negative terminal not connected: the current flow to the ground?( I believe because there is a potential difference 5 - 0 V) but then where the current will go? Is possible that the current flow to one negative terminal of another source(to closing the loop)?

-I don't understand what happen when In a simple circuit, like a battery with a lamp, i connect the negative terminal with the ground ( and with the closed loop circuit) , In this case why electrons don't "flow" to the ground? I think because ground have more resistance, but so why there is the connection?

-The ground is referred as a 0V level, but so if I connect the ground to a 5 V source, the point of connection become 0V?

Thanks for reply

 

[artis]

@lukka98 In order for current to flow there must be a closed circuit. A typical battery is a chemical electricity source , current will only flow if both terminals are used because the current that the battery generates comes from within the battery due to chemical processes taking place. Using just 1 terminal of battery won't allow for current to flow through nor for current to be generated within the battery.

Also and this might be harder to understand but the battery's positive terminal is only positive with respect to the battery's negative terminal because the potential difference exists between those two points. The positive terminal doesn't have to be positive against ground necessarily because the physical Earth is not a reference point for the battery, only it's negative terminal is.

That being said there is one additional factor , namely capacitance, every object has capacitance. Battery terminals are rather close together, so they have a small capacitance between them. The moment you connect the positive terminal to nearby ground or a metal plate for that matter you increase the capacitance between the negative terminal and positive terminal so for a very brief moment during the connection a very small pulse of current might flow and then as soon as the new larger capacitance is charged up this current will stop.

 

[Rive]

There are two slightly different usage of the word 'ground' here.

If i have a voltare source (like a battery) that supplies a 5V voltage difference between its terminals, and there is a parth from positive to a resistor and then to ground, with negative terminal not connected: the current flow to the ground?

In this kind of usage of the 'ground' it is a kind of 'always there' conductor, available anywhere. But still, If you want current then there should be a closed circuit. So you have to connect that negative terminal to the ground too, so current can flow through.

The ground is referred as a 0V level, but so if I connect the ground to a 5 V source, the point of connection become 0V?

In this kind of usage of the word, the ground is the reference voltage. You are right, if you connect it so then the +5V terminal of that battery will be at 0V and the negative terminal at -5V.

 

[anorlunda]

Summary:: I have a few question about Earth grounding that i don't understand.

Is possible that the current flow to one negative terminal of another source(to closing the loop)?

Bingo, that's it. In the circuit below, no current flows out of the plus side of the battery unless an equal current flows into the minus side. At the grounding point d, the current c-d exactly matches the current d-a. In other words, add the ground, or remove the ground and nothing changes.

 

[lukka98]

Ok, but if I grounded chassis of a devices, when there is a fault, the current should flow to the Earth ground (maybe...?), but then where it will go? To the negative terminal through the soil?

 

[anorlunda]

Ok, but if I grounded chassis of a devices, when there is a fault, the current should flow to the Earth ground (maybe...?), but then where it will go? To the negative terminal through the soil?

In some cases current can flow through soil. But they're rare, so it is best to not let them spoil your ideas about closed circuits. Look at the diagram in post #4 and imagine that ground symbol to be the chassis.

To the negative terminal through the soil chassis.

The negative terminal is also connected to the chassis.

 

[lukka98]

OK, and if I have this circuit:

The point where +100V is written is connected to ground, so it is at 0V...(?), also the return is at 0V because it is connected to the ground... how the current flow if there is not potential difference?

 

[artis]

Not sure where you got this schematic but no the + line is not connected to ground , it is connected to ground through a resistor named "R leak" in the schematic.
That resistor can have any value but in reality for practical applications it would have a large value so a high resistance so very little current would flow through it , otherwise if the value was low you would "short circuit" the + line to ground because in this schematic following the symbols it seems that the power supply negative is connected to chassis ground which at the load side is connected to the real ground so if we drew connecting lines between those symbols they would all connect together at one point.

 

[sophiecentaur]

The point where +100V is written is connected to ground, so it is at 0V...(?), also the return is at 0V because it is connected to the ground... how the current flow if there is not potential difference?

By that argument, any load connected across a battery would bring the terminal volts to zero. You made a wrong assumption that any load is a 'short'.

 

[anorlunda]

OK, and if I have this circuit:

Try these 6 circuits. See what the current is in each. Note the voltages, and how they differ from absolute potentials. Voltages are always measured between two points. That may be what is confusing you.

 

[lukka98]

I understand when the ground is placed, and how the current and voltage are measured, but I don't understand the meaning of ground in a "microscopical view";
Well, If I have a battery through a circuit I envision the electron are pumped-in to negative terminal and that creates a "electric pressure" that shove the neighbour and so on to positive terminal, where the potential energy of the electron are at the minimum because of energy "dissipated" in various way, so a potential difference is a potential energy difference.
But if I connect the negative terminal to the ground, that is made of neutral atoms, why the electrons should shove the electrons in the wire of the circuit rather than goes into ground... or shove the valence electron of the soil or others thing.
What means that If i connect to the ground in some point is at 0v? The electron gain or lose energy?

So maybe the main question I have is why the ground is needed? For the fault of circuit I think at this point but I don't understand how this happen in a microscopic view;

For example:

In the first image, I think current flow through the Earth ground to the negative terminal, but also if the path is very very long? this is avoided for some reason but theoretically is possible?

the second resolve the problem for the first to be avoided, but so in that second image what the Earth grounding do? It made the negative terminal at 0V, but why? What happen to the electron pumped-in by the battery in the negative terminal?

 

[anorlunda]

the second resolve the problem for the first to be avoided, but so in that second image what the Earth grounding do?

For the purposes of simple circuit analysis, the ground does nothing at all. You can leave it out and nothing changes.

For the purposes of house wiring, or for purposes of a chassis, the physical ground prevents hazards in case of a wiring error or a malfunction. A wiring error means that things are not wired the way you think they are.

A few places in the world, there are "single wire Earth return" power grids. The current return is through the soil. However, they need an extra 20,000 to 30,000 volts to make it flow. But like I said before, that's rare and should not interfere with understanding of "normal" circuits and power grids.

 

[lukka98]

For the purposes of simple circuit analysis, the ground does nothing at all. You can leave it out and nothing changes.

For the purposes of house wiring, or for purposes of a chassis, the physical ground prevents hazards in case of a wiring error or a malfunction. A wiring error means that things are not wired the way you think they are.

A few places in the world, there are "single wire Earth return" power grids. The current return is through the soil. However, they need an extra 20,000 to 30,000 volts to make it flow. But like I said before, that's rare and should not interfere with understanding of "normal" circuits and power gr

 

[lukka98]

The current flow only through a difference in potential energy, also called voltage, like water at different heigths.
When I connected to the Earth ground the chassis, I connected to a "earth level"'s swimming pool, if there is a fault for the chassis, like it touch the hot wire, the current should flow to the Earth but there is not closed path so why? Is the electron that flow from the Earth to the positive terminal of the source and then to the negative terminal to the ground, so the negative terminal must be connected to the ground?

 

[artis]

@lukka98 stop thinking of electrons , you will get around that concept later on , for all we know from a classical "hands on" approach to everyday circuits is that there is a phenomena called electricity. Electricity is nothing more than just the movement of charge through a conductor created by a potential difference.

So now take this approach and whenever you see one of those simple circuits you posted use arrows and draw either in your mind or on paper where the current would flow. Remember current can only flow in closed paths so if you have a circuit with a battery then you know that current will always flow from the positive terminal to the negative and that's it. No extra added grounds or whatever changes that.
Now the reason current flows from +- is because we (scientists) originally thought like that. Then later on we found that in most conductors like copper wires etc current actually flows from minus to plus. But this thankfully changes nothing you still have a closed path and you can draw an arrow that bites it's own tail.Normally in DC circuits like those that you show there are not added grounds exactly for this reason, the current doesn't flow there. It's the same as I told you at the start, if you connect a battery with its negative or positive terminal to ground no current flows. This is the reason why cars can be left outside in pouring rain and they don't drain their batteries.

To learn this AC is not the best example, start with DC. Because in AC there are such things as impedance and capacitance known commonly as reactance. Every object has some capacitance including ground/earth and that is why if you provide a conductive path for a live AC wire to ground it will conduct some current even in the absence of another ground nearby, simply because the current constantly changes direction and charges/discharges the capacitance.

 

[lukka98]

But If there is a fault, and the classis is connected to hot and to ground, why current flow It the circuit is not closed? I see this in many video and book explanation

 

[lukka98]

If I undestand: the ground is used to place a point of reference, for "default" ground is at 0V, and so other parts of circuit follow that.
But when I connect the negative terminal of a battery with the closed loop and with the ground too, electron go to the wire because they go toward the positive terminal (in the ground there is no electron that ca be' shoved) , is correct?

 

[anorlunda]

Your questions have been answered again and again. Please re-read the answers instead of rephrasing the same question.

 

[artis]

If I undestand: the ground is used to place a point of reference, for "default" ground is at 0V, and so other parts of circuit follow that.

Yes that is what is done in most cases.

But when I connect the negative terminal of a battery with the closed loop and with the ground too, electron go to the wire because they go toward the positive terminal (in the ground there is no electron that ca be' shoved) , is correct?

Forgive me but this makes no sense, you really need to focus more before you think up your questions.

Putting a battery inside a circuit and closing the circuit simple makes the electrons exit the negative terminal and flow towards the positive terminal. This creates current.



I suggest you watch these basic videos both the one in the link and others that are in the suggested feed from the same channel. Watch them thoroughly and if you have any further questions come back and ask them but before you ask them write them down and think them through yourself , this way they will be better and get better answers.

 

[jrmichler]

Your questions have been answered again and again. Please re-read the answers instead of rephrasing the same question.

And on that note, this thread is closed.