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Given the circuit drawn below, why doesn't current just go from the positive terminal of the battery straight to ground as in A. but, rather it goes round and round the circuit from the positive terminal of the battery through the loads and back into the negative terminal of the battery as in B?

two part circuits

It seems to me that +6V would flow through the first load and then on to 0V ground. I'm not an EE and I'm fairly new to electronics, so please keep the explanations direct if not simple.

I ran the circuit in Multisim, and B. is how the circuit behaved, with +3V measured between the positive terminal and the 0V reference, and -3V measured between the negative terminal and 0V reference, or +6V measured between the positive and negative terminals, the circuit draws 3mA.

clarification: I'm asking about the current flow in the circuit, not the polarity of the potentials.

Circuit fantasist
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decuser
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    What comes out from the positive terminal of a battery, must come back to the negative one. In this case, the GND is used here as a reference point. The point from which we measure all our voltage in a circuit. We have a very similar situation when we try to measure a height of an object. We need a reference point. The most common reference point is "above mean sea level". But when you measure the height of the table in your house the floor now becomes your reference point. And in your circuit, GND is the reference point. – G36 Aug 27 '22 at 14:38
  • I asked that one a while back and it's definitely related, but not quite the same. That one was about polarity of voltages, this one's about the path current takes. I kind of get the other one (it's a convention that the ground is a reference point relative to the voltage source which is positive X volts on one side and -X volts on the other). – decuser Aug 27 '22 at 15:04
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    The Ground symbol simply marks the spot in the circuit that we call "Zero Volts, and use as a regerence when measuring voltages elsewhere in the circuit. It does not "suck all the current out of the circuit" - there is no external connection, so nowhere for current to flow to. – Peter Bennett Aug 27 '22 at 16:36
  • I asked two different questions, one about voltage polarity and one about current flow, but somebody thinks they are duplicate questions - how so? – decuser Aug 27 '22 at 17:03
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    It looks like this question was marked as a duplicate erroneously. The answers on [the linked question](https://electronics.stackexchange.com/questions/539589/how-do-you-calculate-negative-and-postive-voltages-in-a-grounded-circuit) don't seem to say anything at all about why current doesn't flow to ground in circuits like this. – Cassie Swett Aug 27 '22 at 17:32
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    NB: GROUND is just a name. It's a reference point. It has no "magic meaning" as regards current flow or voltage difference. A circuit could be deemed to have "GROUND" at any desired node in its circuit. BUT using some nodes as reference points is much more useful than using some others. GROUND may be at actual real world ground, or may not. Often if a circuit is 'real-world-ground" connected then that point will be called GROUND for reference purposes. But it's not essential. As "GROUND" has no properties except those set by the circuit current and voltage are effectively "unaware" of it. – Russell McMahon Aug 30 '22 at 08:18
  • (Connecting real-world-ground to a point in a circuit may alter its behaviour for various technical reasons BUT that does not mean that that connection point is necessarily "Reference GROUND" for the application concerned. – Russell McMahon Aug 30 '22 at 08:22

7 Answers7

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By and large, current has to come from somewhere in order to go to somewhere. For current to come out of the positive terminal of a battery* current has to go into the negative terminal.

It's a principle of electronics (physics, really) that if you draw a circle around any portion of the schematic, then the sum of all of the currents flowing into that circle will equal the sum of all the currents flowing out.

If you draw a circle around your battery and two resistors, then there's only one wire coming out of the circle -- that's the one going to ground. So the current in that wire must be zero.

* There's a slight exception here called "body capacitance". Any conductive body can build up a positive or negative charge -- but only to a point, after which sparks fly (literally). For most circuit analysis, you can ignore it.

TimWescott
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  • Nice! I read somewhere that the telegraphers of old used ground as their return path for current. If I modified my example to have another ground would it then have a path to travel? – decuser Aug 27 '22 at 15:09
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    They used the railroad tracks as the return current @decuser – Andy aka Aug 27 '22 at 16:47
  • "If I modified my example to have another ground would it then have a path to travel?" Yes. Sometimes that ground symbol ends up being a distraction -- to the extent that it has any magic at all, it's because it's connected to the equipment case, or to actual earth ground. But for some newbies it's just a hugely misleading distraction. Ground is just another circuit node: that's it. – TimWescott Aug 27 '22 at 18:33
  • The original telephones used a high voltage to ring the bells to alert to an incoming call. Ground was used as the return. There is a story of a person chaining his dog to the ground rod for the bells, then complaining to the telephone company that they would receive calls only when the dog barked. – RussellH Aug 28 '22 at 03:14
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In most electronincs, "Ground" is simply the point in the circuit that we choose to call "Zero Volts", and use as a reference when measuring voltages elsewhere in the circuit. When used this way, "Ground" does not imply any connection to the earth or to anywhere else outside the circuit.

If you build a battery-operated circuit on a plastic breadboard, you will normally call some point in the circuit "Ground" - usually the negative terminal of the battery. However, depending on the circuit the "circuit ground" may be the positive terminal of the battery, or often with op-amp circuits, the mid-point of the power source, so you can have both negative and positive power supplies.

In AC power wiring and some radio antenna systems, "Ground" will mean "a connection to the earth". In AC power wiring, this may be called "Protective Earth" or "Safety Ground" - it is the third pin in the AC outlets in many countries.

Peter Bennett
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It can be quite easy to understand why current must flow in a loop, and why it cannot just (permanently) flow from the battery into ground without an equal current also entering the opposite battery terminal.

First, note that the battery as a whole is not electrically charged. When we say that the battery is fully charged (as opposed to drained), we do in fact not mean that it has net electrical charge stuck to it. Instead, the positive and negative charges have been separated to both poles of the battery. These charges attract each other, and they'd love to move to the oppositely charged terminal. This force of attraction we can use to perform work.

Next, let us connect the battery to the circuit as drawn in the OP. Assume for some reason, there is a current flowing like you drew it, from the battery's positive terminal, into ground. What would happen?

The outgoing current (flow of charges) leaves the battery positively charged. This will do one (or both) of two things:

  1. it will expel negative charges from the negative terminal
  2. it will suck in positive charges into the positive terminal

In any case the process stops when charge neutraility is restored. The first case effectively stops the outgoing current we assumed in the first place. In the second case, we have now formed a loop, where exactly the same current exits the battery on one side, as enters it on the other.

polwel
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In electrical circuits, current flows in loops. There is no return path involving ground, so no current will go there.

Current may flow briefly from the whole circuit to ground right after you connect them: since there is no loop, eventually the potential at the point of contact will equalize with ground, and this current will stop flowing. That's what electrostatic discharges are.

FrancoVS
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Ground is a voltage reference(0V) , it doesn't affect the circuit at all it is something we use to find the voltage of a node relative to earth,it doesn't need to sink current.

Miss Mulan
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  • I thought current flowed from high potential to low potential - +6V to 0V, is that not the case here? – decuser Aug 27 '22 at 14:40
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    GND doesn't have to be connected with the earth. – G36 Aug 27 '22 at 14:40
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    @decuser The truth is that the current is always flowing in the closed loop path. This means that what's "left" (leave) the positive terminal of a voltage source must return to the negative one. https://i.stack.imgur.com/SSvsu.png – G36 Aug 27 '22 at 14:44
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    @decuser Remember that in the electronic, the ground is just a reference point, not a real Earth ground. And we are measure all our voltage with respect to this reference point, called ground (GND). https://i.stack.imgur.com/nmAMR.png – G36 Aug 27 '22 at 14:45
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    @decuser The positive terminal of the battery, in this circuit, is at 3 V, not 6. – Hearth Aug 27 '22 at 15:23
  • @decuser your previous question has an "accepted" answer that explained this [How do you calculate negative and positive voltages in a grounded circuit?](https://electronics.stackexchange.com/questions/539589/how-do-you-calculate-negative-and-postive-voltages-in-a-grounded-circuit) – Andy aka Aug 27 '22 at 16:51
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Other answers did a thorough job explaining the need for a current to flow in a circuit: a loop. Car racing circuit = car racing loop, as a mnemonic aid. “Circuit” and “loop” are synonyms(-ish).

But the circuit you’ve drawn is also a building block in electronic circuits. There are many uses of it. One is when we need supply voltages that go “around” some signal, ie. are always above and below it, with a fixed voltage (“distance”) from the signal. This is often found in linear bench power supply designs, for example.

Imagine that the “ground” you’ve drawn is the output (+) terminal of a power supply with a range from 0 to 150V. Obviously most ICs like op-amps and small signal transistors won’t survive being powered from 150V. But we can get the +/- 12V supply floating around the output (+) terminal. Instead of batteries, one uses the secondary winding of a mains transformer, an a rectifier.

Another way to “add a floating voltage” in a circuit is with current sources. If there is a resistor somewhere in the circuit, one can connect a current source around it. The current shunted through the resistor will generate a voltage per Ohm’s law, as-if a battery was added in series. This takes a differential output current source (aka a floating current source), and finds some applications in analog circuits, but not only.

Suppose we have a low impedance digital output and want to shift the levels up or down by a fixed offset voltage. Add a series resistor to the output, and have a current source drive current into/out of the resistor. The resistor can be AC bypassed with a capacitor. The “free” end of the resistor will have the logic signal offset by an offset voltage that’s the product of resistance and current (Ohm’s law).

Kuba hasn't forgotten Monica
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The other answers were great, but I got to thinking in terms of a water analogy - given a trench of water with a water wheel, water goes round the trench until the water wheel stops. If you then cut out a mini trench that goes nowhere, sure water fills the mini trench, but once it's full, that's it for that (body capacitance), but the water keeps going around the trench until the wheel stops:

enter image description here

decuser
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