# Electric ground?

#### harshant

I was going through the method of image charges and came up with this "infinite grounded conducting plane". What i wanted to ask is that in reality how do you actually maintain a conductor at zero potential w.r.t. infinity? What does "grounding" mean?

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#### Meir Achuz

Homework Helper
Gold Member
"Grounding" just means that the potential is zero.
Since ilt is a conductor, if any part of it is atg zero potential, then all of it is as far as the eye can see, which is a definition of infinity.

#### harshant

But how do you maintain zero potential w.r.t infinity in real situations? How does connecting the conductor to earth/ground make the potential zero?

#### f95toli

Gold Member
There is a difference between ground and earth. If you have a battery driven circuit you can still define a potential V=0, i.e. ground. The reason is that only differences in potential matter; meaning where you decide to put the zero has no physical significance.

Now, earth is another matter. There are several reasons why we often connect ground to earth. One is simply that mains wiring uses the potential of earth (i.e. litteraly the globe) as zero which means that most electrical equipment does so too. The same is true for e.g. radio transmitters.
One advantage with the earth is that it is pretty big meaning it doesn't really matter if you add or remove a few electrons to it; i.e. it won't get "charged" no matter what.

Getting a good low impedance connection to earth is actually quite tricky; a lightning rod is of course the simplest example (i.e. a metal rod hammered into the ground) but sometimes more sophisticated methods are neccesary. If the soil is very dry it might be neccesary to bury a rather large chunk of metal in order to get a large enough contact area. In some cases salt is added to the soil in order to increase the conductivity.

#### Claude Bile

In addition to potential difference, one can also define an absolute potential, which is the potential w.r.t. infinity. In other words, we can define an absolute voltage based on the energy it takes to move a test charge from infinity to the point of interest.

For the problem of an infinite conducting sheet, it actually takes ZERO energy to move a test charge from infinity to any point on the sheet (by the definition of a perfectly conducting sheet). So the sheet in this case is in some sense "grounded" at infinity.

As f95toli pointed out though, the use of infinity as a reference point is no more significant that using the potential of the Earth, or any other potential for that matter. That is why, rather than bothering to try to set voltages w.r.t. infinity, we choose a common reference point that is most convenient to us, which is typically Earth.

Claude.

#### harshant

I think i got it, thanks guys!!

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