# Current flow with a potential difference

I have a small question, I am trying to wrap my head around the different types of ground connections in electronics.

• For earth ground connection

In an earth ground connection electrons can sink to the earth with only a single connection to earth correct? The way I am viewing it is by looking at it in a CMOS perspective. In CMOS circuits there is dynamic current flow and it is from one of the power rails to the parasitic capacitance on the output, there is no "closed path" but the current still flows. So when we have a basic resistor circuit with one resistor we can follow the same convention, in which charge will flow from a point of higher potential to a point of lower potential, there does not need to be multiple connections to ground to create a closed loop, we only need a single connection from a point of higher to lower potential.

• Floating ground

There is no actual earth connection, it is just a reference point. There will be EHP recombination at this reference point.

My main concern is about the earth ground, one connection should be enough. If we only have one connection to ground lets say it looked like this:

The positive side is at a higher potential than the ground would current flow until there is no potential differences between the source and ground?

• If you pick a small battery and one side of a battery connected via a resistor to the earth's ground and the other side of a battery you left not connected (floating). No current can flow in this type of circuit. – G36 Jan 18 at 19:45
• Your circuit shows a battery with its positive terminal grounded through a 100 ohm resistor. No current will flow until you close the circuit loop. Note that we're ignoring capacitance between the negative terminal and ground as this is negligible in most cases. – Transistor Jan 18 at 19:55
• That dosent make any sense though. Current is based on a potential difference. If there is a conductor and a potential difference current HAS to flow. It will be momentary until the positive end of the source has equal potential in regards to the earth. I think the "closed circuit" convention is something that makes it easier for engineers to visualize, not that it is necessarily needed. Love to hear feedback on this. – Grant Jan 18 at 20:24
• EDIT: That dosent make any sense though. Current is based on a potential difference. If there is a conductor and a potential difference current HAS to flow. It will be momentary until the positive end of the source has equal potential in regards to the earth. This current will be transient. For a continuous current to be flowing there needs to be a closed path so the charge can return to the source. Love to hear feedback on this. – Grant Jan 18 at 20:30
• In your circuit the source's +ve terminal is at ground potential, and the source's -ve terminal is at -1V relative to ground. There is no current flowing, therefore there is no voltage across the resistor. – Chu Jan 18 at 22:55

In CMOS circuits there is dynamic current flow and it is from one of the power rails to the parasitic capacitance on the output, there is no "closed path" but the current still flows.

There is a closed path. The parasitic capacitance allows current to flow (momentarily) when the voltage on one side of it is changing, thus closing the path.

But this doesn't mean it flows with only one connection to the reference node. The power supply needs to connect from the reference node to the Vdd supply of the CMOS circuit, so that a complete circuit is formed, for current to flow.

There will be EHP recombination at this reference point.

Electron-hole recombination only happens in semiconductors. It happens (as a net effect) whenever the product of elecron and hole population densities is greater than the square of the intrinsic population density (i.e. $$\np>n_i^2\$$). It has nothing to do with whether the semiconductor is at the reference point or not.

• So lets say only the positive end of a source is connected to the load and the other side is connected directly to ground, current wont flow from the higher potential to the lower potential? There will be an emf and the wire is a conductor. Thanks for the help! – Grant Jan 18 at 18:23
• It will flow momentarily, through parasitic capacitance, until the unconnected end of the load reaches the same potential as the connected end. – The Photon Jan 18 at 18:25
• Okay, thats what I was thinking. The parasitic capacitance would be between the earth and the other terminal of the source correct? So if we had only one connection to earth ground in a circuit, would the current flow to earth until it is at the same potential as earth, we wouldnt need 2 connections for current to flow momentarily. – Grant Jan 18 at 18:26
• No, between the Earth and the unconnected end of the load. – The Photon Jan 18 at 18:27
• Okay, yes that makes more sense actually. So as stated above with the ground connection, if there was a single earth ground connection than that connection point to the circuit would be at the same potential with the earth. Lets say there was a surge of current that needed to flow, the earth ground would provide a place for this current to sink to momentarily correct? We wouldnt need 2 connections to ground to create a "closed circuit". – Grant Jan 18 at 18:30