Why does electricity seek ground. - Page 1
Forum section: electronics / beginners

author: Mint.
author_rank: Frequent Contributor
timestamp: November 16, 2011, 05:25:08 am
content: Why does electricity seek ground?This somewhat relates to the question about how birds don't get shocked on wires.

author: IanB
author_rank: Super Contributor
timestamp: November 16, 2011, 05:41:43 am
content: Quote from: MintyCondition on November 16, 2011, 05:25:08 amIn short, it doesn't.Electricity is like water on the surface of a pond. It tries to find its level. If you make a hole in the surface of a pond the water will rush in to fill the gap, and if you make a hill the water will flow outwards to level it out.The world around us is a sea of charge, all trying constantly to find its level. So for instance, if you have a static electricity machine like a Van de Graaff generator, that machine moves a whole bunch of excess charge into its dome and that charge is like a hill in the pond, it wants to get back to its normal level. So that's why sparks leap off the dome.Batteries and generators are a bit similar, except they move charge from one side (or one electrode) to the other side (or other electrode). They create a hole exactly balanced by a hill. The charge in the hill now wants to flow into the hole to level things out again. If you connect the hole or the hill to the "ground", then the electricity is trying to equalize with the "ground", but this is just incidental. It's really just trying to balance out a hole with a hill.So there is nothing special about ground except that it is like the level surface of the pond where sometimes you place your measuring stick.

author: Armin_Balija
author_rank: Regular Contributor
timestamp: November 16, 2011, 06:07:50 am
content: Quote from: IanB on November 16, 2011, 05:41:43 amThis sounds like some epic buddhist mantra of balance.

author: IanB
author_rank: Super Contributor
timestamp: November 16, 2011, 06:37:09 am
content: Quote from: Armin_Balija on November 16, 2011, 06:07:50 amAh, you have much to learn, grasshopper.

author: IanB
author_rank: Super Contributor
timestamp: November 16, 2011, 06:46:10 am
content: You can prove that electricity doesn't seek ground by taking a battery and the most sensitive microammeter you can lay hands on. Sit the battery on an insulated surface and try connecting the ammeter first between the positive battery terminal and the ground, and then the negative terminal and the ground. No matter how sensitive your current meter, you will never detect any electricity trying to flow from the battery to the ground.A corollary of this is that there is no such thing as "absolute voltage". There is only a difference in potential between two points. Any voltmeter you find will have two probes, and any reading on the voltmeter can only be the difference in potential between the two probes--wherever they are connected (or not connected). Voltage only ever exists as a difference between two points. Sometimes one of the points is the ground, and sometimes it is not.

author: Armin_Balija
author_rank: Regular Contributor
timestamp: November 16, 2011, 08:30:10 am
content: Quote from: Mechatrommer on November 16, 2011, 08:06:50 amThe earth ground is what we've established to be our Ground reference or 0 V potential difference in relation to itself. If you were to pull the potential below GND you'd have a negative voltage but the potential is still there. It all just comes down to the potential energy between two points.-I think it comes down to mass for gram and the meter is just how far light has traveled in the vacuum of space in 1/?299,792,458 of a second. Basically, all these SI units are just our way of referencing something in nature that we can use to manipulate other things. They're just variables.I guess what he was trying to say even though you can measure voltage, there's no such thing as "voltage." It's merely the amount of potential energy between two points, there's nothing in nature that can be measured that is considered voltage.I think that's what he was getting at.

author: IanB
author_rank: Super Contributor
timestamp: November 16, 2011, 08:31:53 am
content: Quote from: Mechatrommer on November 16, 2011, 08:06:50 amYes, I'm sure. I should qualify the statement of course by saying there will be nocontinuousflow of current. There may indeed be a transient flow for an infinitesimal time.QuoteThe difference in potential is between the battery and ground. Given an available current path any difference in potentials will tend to equalize, and the meter is that current path. If the voltage on the battery is "trying to seek ground" it will flow through the current meter.QuoteSince you introduced it, consider length. You cannot say "this point is 5 meters" or "that point is 10 meters", it makes no sense. You can only say "this point is 5 meters away from that point". Likewise, you cannot say "this point in the circuit is at 5 volts" as that makes no sense either. You can only say "this point in the circuit is +/- 5 volts away from that point".

author: IanB
author_rank: Super Contributor
timestamp: November 16, 2011, 08:40:16 am
content: Quote from: Armin_Balija on November 16, 2011, 08:30:10 amWhat I was trying to say it that voltage cannot be measured as an absolute quantity or property of an object in the way that temperature can. Both temperature and voltage are measures of energy, but while temperature can be measured as an absolute quantity, voltage can only be measured as a potential difference between one point and another point. In theory you could say that some object is "neutral" and has no potential, but you can only determine this with reference to some other object. Given the object in isolation you cannot tell what potential it may have and you cannot ascribe a voltage to it.

author: Armin_Balija
author_rank: Regular Contributor
timestamp: November 16, 2011, 08:56:36 am
content: Quote from: IanB on November 16, 2011, 08:40:16 amYeah, I understood exactly what you were saying, I'm unfortunately not very articulate. I'm working on it though.I always found that quite interesting. My professor was explaining that in a GM plant they had these machines that had 480 V running to it with a floating Ground. The circuit itself only saw 24 volts because it was only reading the difference in potential between a voltage divider in the machine. Several workers apparently got killed while trying to measure the voltage because they saw 24 V and not 480. There was some lawsuit about it a few years back, shame really.

author: ejeffrey
author_rank: Super Contributor
timestamp: November 16, 2011, 09:00:47 am
content: For anyone mathematically inclined, voltage is the integral of the electric field. As we all know, you can always add an arbitrary constant to an (indefinite) integral. This is why the absolute value of voltage at a given point is meaningless: you are free to define it to be anything. In order to get something meaningful out, you need to find the potential difference between two points. For convenience, we usually choose some point in our circuit to be zero volts DC, and measure all other voltages relative to that. However, that choice is essentially arbitrary from a physical standpoint.Also remember current flows in loops. If you have a battery powered lamp, for every amp going from the positive terminal through the lamp to negative, there is an amp going from the negative terminal through the battery to the positive side of the battery. This is true even if you connect the negative terminal to ground -- no current will actually flow through that connection, it will all still flow back through the battery.

author: Armin_Balija
author_rank: Regular Contributor
timestamp: November 16, 2011, 10:22:29 am
content: Quote from: Mechatrommer on November 16, 2011, 10:12:41 amIt's fitting that your picture is Einstein! It's all relative!

author: Unknown
author_rank: Unknown
timestamp: November 16, 2011, 10:27:53 am
content: --Not directly related to the OP--ejef and mecha you are saying slightly different but not mutually-exclusive things.Ejef is referring to the more fundamental and general definition of voltage. According to that voltage is proportional to the work done (energy used) when moving a charge from one point to another. If there is no movement, there is no work and you cannot define voltage. Thats why voltage is more formally referred to as voltage difference, or even more formally potential diferrence as voltage came from Volta, the guy most famous for inventing the battery and whose name was given as a unit of measure to the potential difference betwen two point. Describing it with integrals is another elegant way, but maths follows nature, not nature maths. Moving on....Mecha is taking it to the next practical level of saying that ok, if we know that the difference between two points is so many volts, then if we set one point arbitarily as ejef saidto 0 Volts in our mind, then the other point immediately is at a voltage equal to the potential difference. Mathematically, if |DeltaV| = |Va - Vb|, then if we set Va to 0 Volts then |DeltaV| = |Vb|.Hope this helps with the direction of the conversation.

author: IanB
author_rank: Super Contributor
timestamp: November 16, 2011, 05:44:31 pm
content: Quote from: Mechatrommer on November 16, 2011, 10:12:41 amBut see, that is exactly what is implied by the question in the OP.If you understand that it makes no sense to talk about absolute voltage (I've fixed my post above to clarify), then it automatically follows that there is no universal ground (or point of zero potential) that electricity tries to seek. If it truly is easy to understand that voltage is the difference in potential between two points, then it would not be necessary to ask the original question as posed because the answer would be obvious.I actually don't think it is all that easy to understand, though. Early experimenters struggled for a long time over the connection between static electricity and galvanic electricity, which is yet another angle on the same problem. As a teenager and beyond I found the whole thing horribly complicated and confusing.

author: Zero999
author_rank: Super Contributor
timestamp: November 16, 2011, 06:55:47 pm
content: Quote from: IanB on November 16, 2011, 06:46:10 amThat's not completely true.The battery will have a certain capacitance. When the negative is connected to ground a current will flow until the potential difference between the cathode and earth is 0V, then when the anode is connected to ground a current will flow until the potential difference is 0V. If you keep swapping the anode and cathode connections to ground, the battery will eventually discharge You can prove this by connecting the output of an oscillator with a push-pull output running off an ungrounded battery to earth and measuring the output current.

author: Neilm
author_rank: Super Contributor
timestamp: November 16, 2011, 07:14:47 pm
content: Quote from: Hero999 on November 16, 2011, 06:55:47 pmYou will also get some leakage due to the insulator, either due to contamination on the surface or due to the fact the definition of an insulator is actually something that conducts electricity poorly. (Says the man who solved all his offset problems by connecting the top of a plastic pillar to 0V).Neil

author: IanB
author_rank: Super Contributor
timestamp: November 16, 2011, 07:15:50 pm
content: Quote from: Hero999 on November 16, 2011, 06:55:47 pmWell, indeed I agree, though I was trying to simplify things a bit. I commented in a later post as follows:Quote from: IanB on November 16, 2011, 08:31:53 amIn the case you describe we are really just using the ground as a circuit element in a path from one terminal of the battery to the other. What the electricity is really seeking to do is to equalize the potentials on the terminals of the battery.

author: klem
author_rank: Newbie
timestamp: March 29, 2015, 05:46:26 am
content: Quote from: IanB on November 16, 2011, 06:46:10 amThis doesn't prove anything. You don't understand how a battery works. In a typical electrocell battery, chemical reactions happen at both ends of the battery. One end gives up electrons, and the other end accepts electrons. Chemical reactions at BOTH ends must occur for the current to flow. So obviously if you don't complete the circuit in the battery, nothing is going to happen, in the specific case of a battery, simply because of how the battery works.In other cases, you can observe one-directional flow of charge without any return path to the source, e.g. static electricity, lightning, earthing a leaky circuit. As long as there is a conducting path, and the charge imbalance, the chargers will want to neutralize each other.

author: cs.dk
author_rank: Unknown
timestamp: March 29, 2015, 07:38:33 am
content: Quote from: klem on March 29, 2015, 05:46:26 amWelcome to the forumBtw. this thread is allmost 4 years old

author: helius
author_rank: Super Contributor
timestamp: March 29, 2015, 08:08:00 am
content: Yes, that was quite a notable act of thread necromancy.It's not particularly enlightening to talk about "charge imbalances", though. Charges experience a force along the gradient of the E field, as well as a force perpendicular to their motion in the B field. That's it. If you think about a homopolar (Faraday) generator, there is a conductive path, but the charges certainly don't neutralize.