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### Topic: Understanding Grounds (Read 670 times)previous topic - next topic

#### arduinobeginner101

##### Dec 07, 2013, 11:43 pm
Hello,

I am having a difficult time understanding grounds. Take a basic LED for example. Say you have it attached to some arbitrary pin on the Arduino board and you attach the ground the GND pin. The LED lights up. Why then can't the LED's ground wire attach to some piece of metal elsewhere. That piece of metal has no potential, so why wouldn't it work. I thought the ground is something with no voltage coming out of it that the electrons can flow into.
Can someone explain this to me, please.

Thanks!

#### Grumpy_Mike

#1
##### Dec 07, 2013, 11:55 pm
Quote
I thought the ground is something with no voltage coming out of it that the electrons can flow into.

No it is not.
A ground is short for common signal ground. It is the reference point. If it is not connected it is as we say floating.
See:-
http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html

Would you expect the flashlight to light up in this circuit?

#### arduinobeginner101

#2
##### Dec 08, 2013, 12:14 am
I see from your battery analogy that it wouldn't work. Why though?

#### Grumpy_Mike

#3
##### Dec 08, 2013, 12:23 am
Because there is no path for the current to flow round. You need a circular path, that is why it is called a circuit.
No path no current.

#### arduinobeginner101

#4
##### Dec 08, 2013, 12:27 am
But on an atomic level what is the reasoning? Why then do some grounds connect to the Earth itself then?

#### Grumpy_Mike

#5
##### Dec 08, 2013, 12:34 am
On the atomic level it is still the same no path no current.
Electrons do not just leave their atoms they just shuffle along at about 30 mph. Think of it as a very long train with the carriages bumping into each other. The bump travels much faster than the carriages. So while electrons travel slowly the effect is at the speed of light.

An electron can slip it's atom but is not wrenched from it so unless there is an electron to take its place they do not move. Current is the slipping of electrons round a circuit, no circuit no electron movement.

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