Electronics > Beginners
Talk me through this simple circuit?
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LateLesley:
If any electrical or electronic engineer looked at the second circuit, they would assume that all the ground symbols were connected together. Multiple grounds get complicated, though some circuits do have them. The thing they have in common, USUALLY (but not always), is they are the 0V point in the circuit. It is usually the point where you would measure other voltages from, so is assumed to be 0V.

So your second circuit would differ from the first, as the first circuit would have voltage on that line with 3 resistors, but in the second circuit, it would be read as being connected to the other grounding points in "Ground 1", or at least at the same potential IE 0V.

But there is nothing "special" about it, it IS just a "piece of wire" as in your analogy. The only thing special, is you don't want to be touching it if you touch something else with say 100V on it. otherwise you may get a tingle. :)
timelessbeing:
Some pieces of wire CAN be at ground. But a piece of wire carrying an audio signal, for example, cannot be ground.

The second circuit is wrong. You cannot have two grounds at different voltages in the same circuit. There is one ground (0V) and the other is something else.

Usually, convention is that the negative would be ground.
virtualparticles:
Once again, the ground symbol is a net. The grounds you drew in the second circuit would ALL be connected together unless you used a different symbol for the "ground" on the right side. The symbols are important. They have meaning.
pianovt:

--- Quote ---I feel like i'm still banging my head against a wall, i just don't think anyone is understanding what i mean!
--- End quote ---

We understand you better than you can imagine. Below is a detailed response to each step of your thinking:


--- Quote ---Under these limited conditions, i can see no reason not to substitute the word "ground" with "piece of wire".

--- End quote ---

Do that, it's correct.


--- Quote ---So if you agree with that (i'm sure you won't), surely a circuit could have multiple "pieces of wire"?

--- End quote ---

This, too, is correct.


--- Quote ---In the second pic i have used two (yes, count them, 2!) grounds, on the basis that "ground" can be substituted with "piece of wire".

--- End quote ---

This is where you joined the dark side. Work on this last step of your reasoning. You have made the following logical error:

A. Ground is a piece of wire.
B. I can arbitrarily define any piece of wire in a circuit to be called "ground".

Therefore: I can call all the wires in the circuit "ground".

The fallacy is that you can call "ground" only one node in a circuit.  The word "node" is very important. A "node" consists of all the places in the circuit which are connected to each other only with wires and nothing else. The ground symbol represents a wire. You are free to pick which node you want to call ground, but you get to pick only one.


--- Quote ---So to be clear, in the second pic i'm assuming that ground 1 & 2 are not attached to each other.
--- End quote ---

You have just violated the premise in the beginning of your post. In that premise, you said the following:


--- Quote ---Under these limited conditions, i can see no reason not to substitute the word "ground" with "piece of wire".
--- End quote ---

You said that the ground symbol represents a piece of wire. Then you connected the two nodes in the second circuit together using the "ground" symbol, yet you say that the two grounds are not connected to each other.

If you decide that you want to call some other node in your circuit "ground", then you will have to rename your original ground and give it a different name. Specifically, in your second circuit, you have placed a short circuit across two of the (many) 1k resistors. You "shorted" two nodes.

Make a habit of using symbols like R1, R2, ... Rn instead of just values. In your second circuit, I have no way of referring to a specific resistor unless I draw a circle around it and post that picture.



Mr D:
OK!

You almost understood what i meant, but not quite, sooooooooo........... :

Here are two more pictures.

Would you agree that, in intergalactic space, with no observers within a lightyear distance, the two circuits are equivalent and the choice to place the grounds where they are is completely arbitrary?

........and in fact no ground need even be indicated in the diagram (as long as the ground symbols are replaced with a wire)?

And just to be crystal clear: someone might ask: "if there no observers, why would you even need the diagram?". So let's say for the sake of this thought experiment that a robot needs to mass produce the circuits and will need the diagram for that purpose.



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