# Electric potential easy question

1. Jan 6, 2010

### hangover

The electric potential of the ground is taken to be zero.
We will get electric shock if we complete the circuit by touching the wire and standing on the ground simutaneously.(I know the shoes cannot protect us as the resistance is too small)
But what does this "ground" really mean? Does it apply to any floors we are standing,even those on high rise buildings/those do not contain any electric wires and completely made of thick,insulating material(like plastic)?
I was wondering if there are any grounds where people standing on will never get electric shock(the lethal one)?

2. Jan 6, 2010

### hisham.i

Why you are separating your shoes from ground!
The matter is not because its called a shoes and the ground is called ground, but the matter is in the material things are manufactured from.
If the ground was made of the same material as your shoes so you will never be shocked by an electric shock.
If you want to go through details, you have to understand what do you mean by an electric shock? and how we get an electric shock?
We get an electric shock because current is flowing in our body, and there is a potential difference between our body and the ground, also our body has a resistance say R.. by applying ohms V=R*I a current I will flow in your body which causes the electric shock.
In case of an insulating shoes, the shoes has a high resistance R'..so I=V/(R+R'), and R+R'>>>>>>>>>>big then I=0 so you will never be shocked in this case.
So yes there is grounds where people can stand on and will never get an electric shock!

3. Jan 6, 2010

### Born2bwire

A ground is taken as a neutral resevoir of infinite charge. One of the effects of this is that the ground always maintains a constant voltage reference, which we usually take to be zero by convention. So if you pull off charge from the ground or sink charge into the ground then you do not change the voltage of the ground since it has an infinite amount of charge to begin with.

With that in mind, the Earth is a good ground in most circumstances. Locally, any two points will have the same potential. This isn't true over large distances though, as was discovered when they started laying telegraph, but it's ok for local areas. So anything that has a good electrical connection with the Earth (soil) is a ground. Things can be insulated from the ground though. So a person wearing rubber soled shoes is actually partially insulated, if you were to stand on a rubber stool you would be rather insulated from the ground. If however you were standing barefoot you would have an ok connection with ground. Generally though any electrical system will physically bring up a ground connection (originally created by something as simple as a metal pipe embedded into the soil outside your house).

So your connection to ground has to do with the insulating properties of the possible paths to ground through the materials you are in contact with. Though to be shocked in general just requires you to have a potential difference, you do not need to be grounded for this to exist.

4. Jan 7, 2010

### hangover

thanks. i understand, but so why not the floor of the houses be installed a good insulating material layer or just be made of insulating material(good one), so that no one will get the lethal shock?

5. Jan 7, 2010

### Born2bwire

Because the only condition for a shock to occur is that you have a potential difference. Ground is a common potential that causes a shock because it is often taken as the defacto reference potential for most circuits. However, you as a body always has some kind of potential. It could be zero if you have been bumbling about on or with the ground or grounded obects, but you can also have a potential that is non-zero. For example, if you charge up yourself by scuffing across the carpet you have built up a charge and voltage that is different from the rest of the room which discharges itself when you touch an unlucky object or victim.

So the problem is, there is always a potential difference between you, the source and something else. The source voltage always has a potential difference with respect to the return line. This could be a ground line or it could be a negative hot line. You have a voltage yourself, it could be the same as the return line, in which case the hot source line will zap you, or it could be the same as the hot source line, in which case the return line would zap you (though it may not be as extreme of a zap), or you could be different from both, in which case touching either line would be uncomfortable experience.

The main difference when being shocked when you are in contact with ground is that the ground never changes voltage. So while if you charge up and shock your cat, the discharge is slight because you can only source a small amount of charge before you and your cat are at the same potential difference. However, the ground can eat up all the electrons it wants and it will never change its voltage. So being shorted to ground means you will constantly pull a stream of current from any source that can keep sending the electrons. If you are at least isolated from ground, you can still get shocked for the reasons I stated above but it will be less severe (though I reserve comments on the lethality) because your body will build up/dissipate the charge quickly and no longer pull a current.