Trouble understanding grounding points and potential difference

[vortexnl]

I actually started thinking about grounding points after this video of Dave: 



What I'm basically confused about is the fact that you'll short a circuit if the grounding points are equal, but not if you're probing a circuit that runs on a battery and is disconnected from earth ground.

What I mean is: If the electrons flow from a place of high potential energy to a place of low potential energy, why doesn't the charged side of a capacitor flow to lets say the ground of a circuit if the ground lead isn't connected to the capacitor?

My final question is: How do batteries work when put in series? I know you could put 2 AA batteries in series and your voltage range increases, but why doesn't the plus side of one battery flow into the negative side of the other? Why is there no current flow but just a total increase in voltage?

Many thanks,

Nick

[amyk]

What I mean is: If the electrons flow from a place of high potential energy to a place of low potential energy, why doesn't the charged side of a capacitor flow to lets say the ground of a circuit if the ground lead isn't connected to the capacitor?

Because there is only electron flow if there is a circuit, i.e. there has to be a conductive loop to complete the path. (If the voltage between the two points is high enough, then dielectric breakdown occurs and the electrons will jump between them.)

My final question is: How do batteries work when put in series? I know you could put 2 AA batteries in series and your voltage range increases, but why doesn't the plus side of one battery flow into the negative side of the other? Why is there no current flow but just a total increase in voltage?

Same principle.

[vortexnl]

But still, if I charge a capacitor at 50 volts, the electrons are like packed all together and want to move to a spot with less electrons right? Why wouldn't they just flow if I connected it using one wire to another empty capacitor?

[IanB]

But still, if I charge a capacitor at 50 volts, the electrons are like packed all together and want to move to a spot with less electrons right? Why wouldn't they just flow if I connected it using one wire to another empty capacitor?

They would, and they do. However, the capacitance of one floating plate of a capacitor is much, much lower than the capacitance of the whole capacitor in a circuit. So after just a few electrons have flowed the spot at the other end of the wire that started out with less electrons has now also reached 50 volts and the flow stops. All points that are electrically connected, in the absence of outside forces, are equalized at the same voltage. If they start out at different voltages before you connect them then electrons will flow until equalization is achieved.

[vortexnl]

Okay, I have a final question. What happens on a atomic scale when you put 2 batteries in series? What happens to the point where the 2 batteries meet, there shouldn't be electron flow right? I'm just so confused about this.

[IanB]

Okay, I have a final question. What happens on a atomic scale when you put 2 batteries in series? What happens to the point where the 2 batteries meet, there shouldn't be electron flow right? I'm just so confused about this.

The traditional way of resolving this question is to separate electricity into two kinds: "static electricity" and "flowing electricity".

In electronic circuit design and analysis we normally only care about flowing electricity, and for electricity to flow it requires a circuit (a circuit is a closed loop that you can trace round and get back to the same starting point).

So if you put two batteries in series but leave the other ends unconnected there is no circuit. Since there is no circuit, there is for all practical purposes no flow of electricity. So the answer to what happens is essentially, "nothing happens". There is no electron flow that can be measured by normal instruments, nor that makes any material difference to anything nearby.

The best way to avoid being confused by this is to do what every good engineer does and make simplifying assumptions. We restrict our view of the world only to those things that concern the matter at hand and we ignore those things that we don't need to worry about.

It's like if we are driving a car. We care about the controls of the car and how the car responds to our actions. We don't need to care about how the engine works internally, as long as it is going. Knowing how an internal combustion engine works is not part of successfully driving a car from home to work. In our mind we automatically know this and we don't worry about it.

So it is with electricity and electronics. There needs to be a circuit for something to happen. If there is no circuit nothing is going to happen and we can ignore anything after that.

(Of course someone might tell me that there are exceptions and that this is an oversimplification, but IMHO the exceptions get more into the realm of physics than of electronics. And electrostatic discharge or ESD can be a bother with sensitive components, but this is more about workplace hygiene than about circuit design.)

[Teneyes]

And electrostatic discharge or ESD can be a bother with sensitive components, but this is more about workplace hygiene than about circuit design.)

Oh, I remember leaving 400mfd Caps charged to 200V for the High school physic teacher to clean up   he knew it was me,