# Closed loop circuit vs open loop circuit can current flow?

So this has been bothering me. Lets say we have a circuit which looks like this below:

If the connection to ground is earth ground, and the positive side of the voltage source is connected so there is a potential difference over the resistor, would current flow to ground with a SINGLE (just one connection important!) to ground. This circuit would be considered an "open loop" in the conventional sense. Thanks!

• In your example, no. Not continuous current as you know it. This would be like water trying to circulate continuously in a looped pipe with a pump somewhere in the middle...except the pipe is blocked off somewhere along its length. A momentary equalizing charge (we don't really call it current in that context) can flow in the same way water fill flow into an empty bucket (or dead end pipe). That is what most antennas are. There are multiple layers of complexity and the simplest one introduced is that "current must flow in a loop", or at least continuous current anyways. Jan 18, 2020 at 20:15
• The momentary charge would flow until the source and the ground would be considered to be the same potential correct? Where Im going with this is when we connect the chassis of a device to a single ground connection, and lets say a power rail somehow got connected to the chassis, then the current would flow through the chassis to ground without the need for an "closed circuit". Thats what the circuit up there is trying to demonstrate. Jan 18, 2020 at 20:17
• Voltage is always measured relative to something else, so prior to connection the positive and negative terminals of the supply will be floating at some offset to your earth, whatever it is. When you connect the + terminal to GND, a momentary equalizing charge will flow to earth (or from earth) to cause the + terminal to be at the same potential as earth. Since the - terminal is always some constant voltage relative to +, it follows accordingly. So in other words, yes, you can think of it that way. Jan 18, 2020 at 20:19
• Great explanation, really appreciate it. Have a nice day! Jan 18, 2020 at 20:22

## 1 Answer

In your example, no. Not continuous current as you know it. This would be like air trying to circulate continuously in a looped pipe with a pump somewhere in the middle...except the pipe is blocked off somewhere along its length. A momentary equalizing charge (we don't really call it current in that context) can flow in the same way air fill flow into an empty tank (or dead-end pipe) and pressurize it. That is what most antennas are. There are multiple increasing layers of complexity and the first one introduced is that "current must flow in a loop". What is often omitted for simplicity is that continuous current must flow in a loop.

The momentary charge would flow until the source and the ground would be considered to be the same potential correct? Where Im going with this is when we connect the chassis of a device to a single ground connection, and lets say a power rail somehow got connected to the chassis, then the current would flow through the chassis to ground without the need for an "closed circuit". Thats what the circuit up there is trying to demonstrate.

Voltage is always measured relative to something else, so prior to connection the positive and negative terminals of the supply will be floating at some offset to your earth, whatever it is. When you connect the + terminal to GND, a momentary equalizing charge will flow to earth (or from earth) to cause the + terminal to be at the same potential as earth. Since the - terminal is always some constant voltage relative to +, it follows accordingly. So in other words, yes you can think of it that way.

Getting shocked by static is something similar. It's the pressure suddenly releasing and equalizing.

If a source you connected this to is AC instead of DC, then this momentary equalizing charge flows back and forth repeatedly trying to equalize the charge in "the dead end" which would be the negative stub of your power supply in this case. This is what most antennas basically are.

It is similar to repeatedly dumping and sucking water into and out of a bucket.

Note that this is contrasted with continuous AC current which also has an oscillatory nature but does flow continuously in a loop. There's no real mechanical-analog for this...unless you think of alternating localized pockets of higher and lower pressure air circulating around inside a pipe loop. But in real life the air pressure distribution would equalize. out inside the pipe loop. I think it would have flow at supersonic speeds so the pressure distributions won't dissipate. Strangely, it begins to feel start to feel similar to electrical transmission lines where you also can no longer ignore the speed of propagation.

• Appreciate it, the way im viewing it in continuous current context is there is a water reservoir and we dump it out to "earth" or a pool instead of allowing it return to the reservoir after leaving. In both cases current will flow but only in the closed loop case will it be continuous, in the case where it is just connected to ground the charge that makes the voltage difference (the water in the reservoir) will be lost and it will not be able to conduct anymore. Jan 18, 2020 at 20:28
• @Grant Yes. No continuous current will flow without a loop. But connecting things to to "dead-ends" that still maintain an open-circuit will briefly cause a momentary equalizing charge to flow to equalize the potentials. Jan 18, 2020 at 20:31
• If a source you connected this to is not DC but AC, then this momentary equalizing charge flows back and forth repeatedly trying to equalize and that makes an antenna. Basically repeatedly dumping and sucking water out of a bucket. But for this to happen the AC source needs to be fixed at a potential (i.e. grounded) at one end and dead end needs to be where the momentary charge flows. Continuous AC current can flow in a loop despite the oscillatory nature loop but there's no real water-analog for this unless you think of alternating water and air pockets circulating around in a pipe loop. Jan 18, 2020 at 20:34
• Interesting, that makes sense though as the source will be continuously changing potentials allowing current to flow back and forth from the ground connection. I haven't heard about the antennas Ill look into that! Jan 18, 2020 at 20:34
• @Grant I edited my comment. Re-read. Jan 18, 2020 at 20:37