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What is the difference between the below two circuits?

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I know the bottom circuit has 'ground', but what does that mean exactly? Why would someone want to construct the second circuit over the first? And, what would be an example of doing the bottom on a breadboard -- where does ground 'go'?

Finally, when doing the above in EveryCircuit, the first example doesn't even work, or allow current to flow through it. Why is this? (The same circuit works on my breadboard).

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    \$\begingroup\$ no difference electrically ... the bottom shows which node is used as a reference point ... EveryCircuit does not make assumptions about the location of the reference point ... you can put the ground on top also \$\endgroup\$ – jsotola Jan 13 at 1:37
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There is no functional difference in reality. However, your simulation software is stupid and needs to do calculations, so you need to tell it which node you want to represent zero and will become the reference to which every other node is measured (remember that voltage is a potential DIFFERENCE).

The circuit with a GND connection has designated that node as zero volts, he node with which all other nodes are measured with respect to.

Note that physically making that GND connection to something else in reality doesn't make your circuit operate any differently, but does make it so your circuit doesn't "float" if you are using a battery source or some other isolated source. It anchors your circuit to a known potential and not doing so can become an issue for things like noise, shielding, EMI, and safety (arcing for high voltage things).

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  • \$\begingroup\$ "it can become an issue".... Can go both ways. Sometimes the ground helps and at other times it is a source of problems. (On mobile it posts the comment when I try to insert a newline) \$\endgroup\$ – rew Jan 13 at 16:00
  • \$\begingroup\$ I read a very amusing (but serious) note about grounding in high speed (not relevant here, I know, but informative): When my students ask me how to use ground, I say, 'Ground is a good place to grow potatoes and carrots." sigcon.com/Pubs/edn/HiddenSchematic.htm \$\endgroup\$ – Peter Smith Jan 13 at 16:11
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Here, as in most electronics, "Ground" simply marks the point in the circuit that we want to call "Zero Volts", and use as a reference when measuring voltages elsewhere in the circuit. It does not usually imply a connection to the earth - we can talk about Ground in portable equipment, or in battery-powered circuits on a plastic breadboard.

The Ground symbol has no effect on the operation of the circuit, but is usually required by circuit simulator programs so that they know what point to use as a reference when calculating voltages elsewhere.

In AC power wiring and some radio antenna systems "Ground" (particularly the green "Safety Ground") does indicate an actual connection to the earth.

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    \$\begingroup\$ Earth is Earth, ground is ground, do not confuse the two \$\endgroup\$ – crowie Jan 13 at 3:38
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    \$\begingroup\$ @crowie It's a bit location dependent. I've seen schematics where the EU version would say Protective Earth (PE) and the US version would say Ground (GND). \$\endgroup\$ – Mast Jan 13 at 10:46
  • \$\begingroup\$ @crowie perhaps you could expand on that in a way that would help the questioner? \$\endgroup\$ – jonathanjo Jan 13 at 20:34
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Many simulators compute all voltages relative to some "ground" node, and require that some node have a voltage which is set relative to ground. To accommodate schematics where some groups of nodes are "floating" relative to ground, however, simulators will can often identify islands that don't have any ground connection and, if any art found, select some arbitrary node in each island and set its voltage to 0 relative to ground.

In the upper schematic, if you were to attach scope probes to the ends of the resistor, they might report readings of +1.0V and 0.0V, or 0.0V and -1.0V, or possibly (though I've never seen such behavior) +0.5V and -0.5V. In the second schematic, however, the voltages would definitely report +1.0V and 0.0V. In the third schematic, the upper portion's voltages are all measured relative to ground, but the lower island's voltages are not. Thus, a simulator would treat the lower island like it treated the second schematic, adding a "ground" node connection.

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  • \$\begingroup\$ I think you are making some assumptions about where the ground leads from the scope probes are connected (or not connected). Could you clarify that? \$\endgroup\$ – Elliot Alderson Jan 13 at 21:19
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There is no functional difference inside the circuit, the same 1V potential will take effect on the specified resistor, but there can be a big difference from an external point of view.

In the 1st case, your 1V difference can be generated by multiple methods: Having a +1V and 0V, having a 0V and -1V, having a +0.5V and -0.5V or any values that give the difference of 1V. Although not largely in use, some circuit boards today still use +12 and -12V to obtain a 24V potential.

In the 2nd case, you can only have a +1V and 0V (the specified grounding).

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    \$\begingroup\$ Your description of the first case is not correct...you are assuming that without a ground we can measure the voltages at the two nodes independently, with respect to some magical absolute zero voltage. In the absence of an explicit zero reference (a ground symbol) all we can do is measure the voltage between two nodes, not the voltage at a node. That's the entire motivation for adding a ground symbol. \$\endgroup\$ – Elliot Alderson Jan 13 at 14:21
  • \$\begingroup\$ @ElliotAlderson I upvoted your comment in the most part, but have to query the last statement - surely in some circuits the ground symbol is used because an actual physical connection to ground/earth is required? This one is so simple that we cannot tell which possibility the draftsman intended. \$\endgroup\$ – Mike Brockington Jan 13 at 16:33
  • \$\begingroup\$ @MikeBrockington Yes, you are right, there are some circumstances that require a protective earth ground for safety, such as installations of mains in buildings. I suppose some antenna installations might need an earth connection. Strictly speaking, a ground that is not actually earthed is a chassis ground and should use a different symbol. \$\endgroup\$ – Elliot Alderson Jan 13 at 18:21
  • \$\begingroup\$ @ElliotAlderson If yours is the downvote it may be a bit hard on him. I think your query re his correctness may be due to a language issue - when he says "there can be a huge difference from an external point of view, I suspect that he means that it the shown circut's potential is measurd between some point and an external "ground" the difference may be 230 VAC, or 1000 VDC or .... , as there is no formal means of controlling the potential relative to the reference point. \$\endgroup\$ – Russell McMahon Jan 14 at 10:57
  • \$\begingroup\$ @Elliot Alderson You can determine that information by checking the source generating it. \$\endgroup\$ – Overmind Jan 14 at 12:06
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There is no any difference between these two circuits in this case.

But the position of ground has significant role in the circuits. The ground in a electrical circuit is the node where we have our "zero volts".

Pre-Information: A battery is something that maintains a certain potential difference across its terminals depending upon its rated capacity. A 1.5V battery keeps its +ve end at 1.5V higher potential than its -ve end. If I have 0V at its -ve end, I have 1.5V at its positive end. If I have 10V at its -ve end, I have 11.5V at its +ve end and so on. Notice how the +ve end is always higher than -ve end.

Keeping this in mind consider two batteries connected to each others as shown;

schematic

simulate this circuit – Schematic created using CircuitLab

In first figure, the ground is connected to -ve terminal of 1V battery and +ve terminal of 2V battery.Since we refer to ground as our 0V, the -ve end of V1 and +ve end of V2 is 0V. So, you get the +ve end of V1 to be 1V greater than -ve end of V1. So, you have 1V at node A. In case of V2, the +ve end is at 0V. So the -ve side must be 2V lower than the +ve end. So, you get -2V at node B.

In case of second figure, we have the -ve side of V2 grounded(0 volts). So the +ve side of V2 is 2V higher than the -ve side. Meaning 2V at node C. Also, the -ve end of V1 is connected to +ve end of V2(which is at 2V). Since V1 is 1V, it should maintain its +ve end at 1V higher potential than -ve end. This implies we have 3V at node A.

This is how you can see the difference between your two circuits. The ground and -ve end of battery may or may not be at same node. The ground can be placed at +ve end of battery as well. But this gives -ve voltage at your -ve end.

Hope this helps!!

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