Question

Hi all,
I am a little confused with a charge flow for the case when a negatively charged body is connected to the earth. If the Earth has net negative charge, why the electrons from the body go to the ground anyway?

Answer 1

well earth has no charge and it is considered to be at zero potential also a big capacitor that can store huge amount of charge...so whatever extra electron is developed and if connected to ground, all the electron flows into the ground

Answer 2

Hi Ghazi,
Thank you for your reply.
I know that the earth is considered to have a zero potential, but why it has no net negative charge? I haven't found a good description for this problem, but you can use the link below for the reference (just a few paragraphs in the begining):
http://vixra.org/pdf/1008.0071v1.pdf
Moreover, there is an electric field which points downwards near the Earth's surface with a magnitude of about 100-150 V/m. This is because of net negative charge on the surface and net positive charge on the clouds.
As long as I understand, the charge of -4.5x10E5 C is distibuted on the surface of the planet. Let's assume a uniformal distribution to ease the calculations. Then the surface density is the charge divided by the area of a sphere with R=6400 km:
4.5x10E5/(4*pi*6.4*10E6*6.4*10E6) = 8.7*10E-13 C/m2
This density seems to be extremely small, so any negative charge produced by e.g. rubbing can easily flow to the ground as you described to the point with a zero potential. In case if a positively charged object is connected to the ground, then the electrons are sucked on it.
There is no such an explanation in the books I have, so I just wanna be sure that my understanding is correct.
Please let me know if there are any mistakes.

Answer 3

as far as i understood charges flow from higher potential to lower potential
and not towards the opposite charges i mean they do flow towards opposite charges but they can also flow towards the same charge provided the potential of the surfaces is different

Answer 4

@Yury when i dig more and more...then at the most fundamental level i get confused ..do positive charge exist ...?? actually i mess up with concepts of atom having positive charge which means lack of electron, concept of charge in semi conductor (that is hole) and concept of charge in quantum mechanics

Answer 5

@ghazi
Sorry for confusing you) I haven't dug such deep for semiconductors and quantum mechanics, but this particular problem, as long as I see, can be described without these concepts (at least on a low level) . The deal is that the charges are separated and some of them are on the clouds, and the opposite are on the Earth's surface. If my understanding is correct, then negative charges flow from a charged object to the ground because the last one has a higher potential, just like RajshikharGupta wrote.

Answer 6

Yes, the Earth has a charge. However, we assume that Earth is at a relative zero potential. "Relative" is the key term. If you have a 12V battery, then you would say that the battery and Earth have a potential difference of 12V. You are describing the electric field between the battery and the Earth's charge density. For all practical purposes, the Earth's charge density does not change; therefore, it makes a good standard to make measurements against. If you measure 12V on a battery, then fly to the other side of the world, what would you expect the voltage to be? You would expect it to be 12V because the Earth's charge density is consistent and unchanging.

Answer 7

well as far as cloud is concerned ..it is the formation of negative charge that takes place in cloud (not fully understood how?) and that negative charge induces equal amount of positive charge on the surface of earth (charging by induction) now these act like two plates of opposite charges and due to very high potential difference (1500KV) it ionises the air between clod and surface of earth and in this way electricity flows to the ground (the path of current is ionised air)....

Answer 8

and to flow charges from one point to another there is need of potential difference...if there are two charged plates one having 100e and other having 1000e then there will be flow of electrons from 1000e plate to 100e...the basic thing to flow current is potential difference ....similarly if earth has negative charge but if the the object or the conductor connected to it has higher amount of negative charges then ..extra negative charges will flow to the ground...

Answer 9

I think the importent subject is potential difference,I saw much examples that flow charges from earth to a charged object,and flow charges always from higher potential to lower potential.

Answer 10

our body is at higher potential than the earth(which is at 0 potential) and we know that -ve charge move from lower to higher potential and vice versa so the charges(+ve) from earth climbs up and neytralizes the -ve chage on the body..

Answer 11

@ghazi:
But the total charge of the Earth is 4.5x10e5 C, which is much greater than we can produce by e.g. rubbing. And that means that the electrons should flow in the opposite direction, which is not correct. I am trying to describe it with terms of surface density and initially diffirent potentials, but still can't put it all together.
@chrsimmo:
1. As our body is a conductor, we should have the same potential as the Earth (let there be no shoes), do we?
2. A little deeper battery question. Do we really have a potential difference of 12V between the ground and the terminals? As long as I understand the classic Volta's battery principle, both terminals have the negative potentials, but one of them is just more negative than another, so the total difference is about 1V. Is it ok?
@Amitshukla
how the positive charge can move from the Earth if they are fixed? Moreover, there is an excess of electrons, so they wouldn't let the positive charge go anyway.

Answer 12

@Yury i didn't say anything has charge more than earth by that i mean to say...if for an instant we consider that charge on an object is more or relatively higher than that of it's counterpart then from higher to lower charges will flow...now earth has charge but is at zero potential that's why extra charge flows to the ground. And as per your concept if earth has higher amount of charge then we must have felt shock but that's not true...(as you said that earth has huge amount of charge)....surface of earth has got no charge that's why negative charge flow down

Answer 13

@Yury:
1) I do not know what the charge density of a human body is, however, it is very likely that it's not the same charge density as the Earth. So there will be a potential difference. Yes, current would flow from our body to Earth, but it would be very, very small. Think about Ohm's Law.
\[V = I*R\]
\[I = V/R\]
The resistance of the body is very high (~1kohm to 100kohm) and the voltage is small (sorry, I don't have any idea what voltage may exist between the body and Earth); therefore current will be very small, according to Ohm's Law.

My point is that charged particles cannot discharge very quickly from the body into Earth but you can collect a charge very quickly. Just think about taking off a sweater. That simple action can give you enough charge to cause an electrical discharge from your finger to something metallic.
As far as calling the body a conductor, I don't think that I would consider it a conductor. A "conductor" just describes a material with a high conductivity whereas an insulator has a very low conductivity.

2)
So maybe the battery analogue wasn't the best example. I didn't think that anyone would think too deeply about that one. It sounds like you understand the basic principle of a battery. As long as there's an electrical path from the positive terminal (high electric potential) to the negative terminal (low electric potential), then charge will flow. Basically, the electrons on the positive terminal flow through the circuit to the negative terminal. It depends on the battery type/chemistry, but the electrons may recombine with a positive ion.