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schematic

simulate this circuit – Schematic created using CircuitLab

I am trying to apprehend the concepts of "ground" in electric circuits. There are some excellent answers on SE here on this topic and they have been very helpful. I am now quite comfortable with "ground" as a reference point. However, with the idea of using direct physical connection to earth in circuits, not so much. In simulators, for example, the two circuits above will give the same reading of current through the resistor. My question is, if I take two batteries, two bulbs and two one-meter wires and make two circuits as above, will their behavior be identical?

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  • \$\begingroup\$ They are the same in operation, but they are the same in analysis only if a specific assumption is made. \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Commented Jul 12, 2015 at 16:45
  • \$\begingroup\$ This is a sign of common i.e a very low resistance conductor connecting points, and it is used to avoid mesh in a schematic making this easly readable. \$\endgroup\$
    – GR Tech
    Commented Jul 12, 2015 at 19:12
  • \$\begingroup\$ @GRTech I am not talking about the common reference point here. In the first circuit, by ground I mean the literal insertion of the wire into earth. From Wikipedia ground article, for example: "In electrical engineering, ground or earth is the reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the Earth.". I am taling about the last type -"a direct physical connection to the Earth". Hence, my question is, will there be a difference if we connect the two end with a conducting wire vs via earth? \$\endgroup\$
    – Lavya
    Commented Jul 13, 2015 at 6:11
  • \$\begingroup\$ @IgnacioVazquez-Abrams What assumptions? an what will happen in practice if we make circuits like the above two? will they perform the same? (assuming earth is wet or whatever it takes for it to be at it's usual best conducting state. \$\endgroup\$
    – Lavya
    Commented Jul 13, 2015 at 6:13
  • \$\begingroup\$ They are the same in operation. How they differ in analysis depends on where you place the ground in the second circuit. \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Commented Jul 13, 2015 at 6:15

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There is no difference, the circuit is the same. The ground symbol is a global symbol, so you don't have to connect all gnd points- there are lots of them.

About the concept- it's probably thebonly way to understand a circuit- having one point for reference for all components (at least within certain circuit). Note, that in the beginning the circuits that students learn don't have any ground.

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  • \$\begingroup\$ Thanks. I understand the significance of the ground symbol and it's use as reference point to some extent. However, I have doubts about the use of real ground (earh) in circuits. Are you saying that whether we buried two end points to earth (deep enough) or joined them (as done in the two diagrams above), won't make any difference? If we have two batteries and bulbs of same capacity, they will glow to the same intensity and for the same amount of time? \$\endgroup\$
    – Lavya
    Commented Jul 12, 2015 at 17:15
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    \$\begingroup\$ In the greater scale of things, the earth potential is the same all over the earth. Some power line arrangements do use the earth as return conductor. However, this depends on good contact to the earth. I think this arrangement is only used for high voltage applications over long distances. I don't think it'd work very well to power a flashlight by by putting two ground leads a few cm in the grass :-). \$\endgroup\$
    – avl_sweden
    Commented Jul 12, 2015 at 17:34
  • \$\begingroup\$ Also, the ground symbol usually doesn't refer to an actual earthing rod. \$\endgroup\$
    – avl_sweden
    Commented Jul 12, 2015 at 17:38
  • \$\begingroup\$ No, don't confuse the things. Earthing is something else, earth potential is not the same- think, what happens if you put Ohm-meter across ten meters of ground. Also Earthing is more elecrical stuff, safety, etc. In electronics we usually just remember that it exists and let the specialists tale care of that :) \$\endgroup\$
    – user76844
    Commented Jul 12, 2015 at 17:50
  • \$\begingroup\$ The ground return was common in early telegraph signalling and such to save on the number of conductors, as mentioned still used in HV transmission lines, as RF antenna counterpoises and as protective earth return for fault and lightning currents. Circuit commons are sometimes connected to earth/ground for various reasons, not all are valid or useful. \$\endgroup\$
    – KalleMP
    Commented Jul 12, 2015 at 20:05

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