# What is ground and what does it do?

All QuestionsCategory: Electrical EngineeringWhat is ground and what does it do?
I’m a little confused about the concept of ground, and possibly voltage as well, especially when trying to analyze the circuit. When I learned about Ohm’s Law in elementary school, I learned how to apply the law to calculate the current, voltage, and resistance of simple circuits.
For example, if we are given the following circuit:

We may be asked to calculate the current passing through the circuit. At the time, I was simply calculating (based on the given rules) 1.5V/1Ohms = 1.5A.
Later I learned that the reason the resistor voltage is 1.5V is that the voltage is really the potential difference between two points, and that the potential difference across the battery will be the same as the resistor potential (correct me if I’m wrong), or 1.5V. But I got confused after introducing the concept of land.
The first time I tried to perform the current calculation for a circuit similar to the previous one on a simulator, the software complained of no ground voltage sources and “floating voltage sources”. After a bit of research, I learned that circuits need a ground as a reference point or for safety reasons. It was mentioned in one interpretation that one can choose any node for ground, although it is customary to design circuits, so there is an “easy place” to choose ground.
So for this circuit

I picked up ground from below, but would it be a good idea to pick up ground between a 7 ohm and a 2 ohm resistor – or somewhere else? What is the difference when analyzing the circuit?
I’ve read that there are 3 typical earth symbols with different meanings – structure floor, ground floor, and sign ground. A lot of the circuits I’ve seen used in drills either use ground ground or signal ground. What is the purpose of using the land? What is a connected earth signal?
Another question: Since the earth has an unknown potential, wouldn’t there be a current flowing from the earth to or from the circuit? From what I’ve read, we treat ground as 0V, but wouldn’t there be some sort of effect due to a difference in circuit voltage and ground? Will the effect be different depending on the floor used?
Finally: in nodal analysis, one usually chooses a ground at the negative terminal of the battery. However, when there are many sources of voltage, some of them are “floating”. What is the meaning of float voltage source voltage?

2 Answers

The first time I tried to perform the current calculation for a circuit similar to the previous one on a simulator, the software complained of no ground voltage sources and “floating voltage sources”.

Your simulator wants to be able to do its calculations and report voltages per node for some reference, rather than having to report the difference between each potential pair of nodes. It needs you to tell it which node is the reference node.
Other than that, for a well-designed circuit, the “ground” has no significance in the simulation. If you design a circuit in which there is no DC path between two nodes, the circuit will be unsolvable. Typical SPICE-like simulators solve this by connecting additional resistors, typically 1 GOhm, between each node and ground, so it is conceivable that the choice of ground node could artificially affect the results of a very high impedance circuit simulation.

I picked up ground from below, but would it be a good idea to pick up ground between a 7 ohm and a 2 ohm resistor – or somewhere else? What is the difference when analyzing the circuit?

You can choose any node as your reference land. We often think ahead and choose a node that will remove the terms of the equations (by setting them equal to 0), or simplify the schematic (by allowing us to denote the connections through a ground symbol rather than a set of lines connected to each other).

I’ve read that there are 3 typical earth symbols with different meanings – hull ground, ground floor, and signal ground. A lot of the circuits I’ve seen used in drills use ground ground or signal ground. What is the purpose of using the land? What is a connected earth signal?

Ground floor is used to refer to a connection with something that is physically connected to the ground under our feet. A wire runs through the building down to a copper rod going into the ground, in a typical case. This land is used for safety purposes. We assume that the person handling our devices will be connected to something like the ground with their feet. So ground ground is the safest circuit node for them to touch, because it won’t drive currents through their bodies.
The chassis ground is just the potential of your circuit can or enclosure. For safety purposes, it is often best to connect this to ground. But calling it “structure” instead of “ground” means you didn’t assume it was connected.
Signal ground is often distinguished from (and partially isolated from) ground to reduce the potential for currents flowing through ground wires to disturb important signal measurements.

Another question: Since the earth has an unknown potential, wouldn’t there be a current flowing from the earth to or from the circuit?

Remember, a complete circuit is required for current to flow. You will need connections to ground the ground in two places so that current flows in and out of your circuit from the ground. Realistically, you would also need some sort of voltage source (battery, antenna, or something) in one of these communication paths to get any continuous flux back and forth between your circuit and ground.

However, when there are many sources of voltage, some of them are “floating”. What is the meaning of float voltage source voltage?

If I have a voltage source with a value of V between nodes a and b, then that means the potential difference between a and b will be volts. An ideal voltage source will generate whatever current is required to achieve this. If one of the nodes happens to be grounded, it immediately gives you the value at the other node in your reference system. If none of these nodes are “ground”, you will need some other connections to determine the value of the voltages at A and B with respect to ground.

Sometimes people are confused just by the many definitions of the word.
Land
Noun
hard ground surface. Hard or dry ground: to fall on the ground
Often, reasons. the basis or basis upon which the belief or act is based; Reason or reason: Reasons for dismissal.
In the context of electronics, earth sometimes means meaning 1 above. Earth is, after all, roughly 6-1024kg6x1024kg a ball of iron. Like anything else, it is in some electrical potential, and if you stick a long conductive rod into the ground, you can create other things connected to that rod with roughly the same potential:
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Of course, the Earth is really big. Not all of it has the same potential. In fact, not even close. The Earth’s huge magnetic field is constantly changing, stimulating currents throughout the Earth. Other people have their own rods stuck in the ground and causing currents in the ground. Lightning stirred a massive current in the earth. Since earth is not a perfect conductor, and by Ohm’s law any current passing through any resistance is accompanied by voltage, the potentials between two points on earth are not the same, unless you are lucky, or the points are very close to each other.
And if you’ve ever powered a battery-powered device, you know that electronic devices can work just fine without contact with the ground. However, these devices have a floor. So, this is probably not the ground sense you should use as the basis for your electrical understanding. The other meaning, the basis for the belief, is perhaps a better start.
It’s a very clever observation that your confusion includes voltage as well. Earth is, simply put, 0V0V. But to really understand what this means, one must really understand effort. Many people fall into the trap of thinking that since the ground is 0V0V, the ground is where there is no voltage. Thus, there must be effort everywhere else. But once you understand the effort, you see that this cannot be true.
So what is the voltage? The stricter term is the electric potential difference. All three words are part of understanding effort. Electricity is clear.
What about the capabilities? Potential has a specific meaning in physics. Potential energy is the ability to arrange certain things to do work. For example, a compressed spring, an extended arc, or a high-pressure gas tank has the ability to do work, if released.
Imagine a ball on top of a slope. If the ball is allowed to roll down the ramp, it will move downhill very quickly. This kinetic energy is gained from the potential energy that was at the top of the slope. If there are no other losses (friction, for example), then the kinetic energy gained by the ball is equal to the potential energy lost, by the law of conservation of energy.
This is potential energy. Only the potential itself has a different definition: it is the potential energy of each unit of things at some point in the system. Obviously, the big ball at the top of the ramp has more potential energy than the small ball at the top of the ramp itself. So, the two balls have different potential energies at the top of the ramp, but they are in the same potential.
The type of related stuff depends on the type of potential. For gravitational fields, matter is mass. For electric fields, matter is a charge. Potential energy is measured in joules. The gravitational potential is measured in J/kgJ/kg. The voltage is then measured in joules per coulomb (J/CJ/C), which is actually the definition of a volt.
We said earlier that voltage is the electrical potential difference. What is the difference? Imagine again our slope. If you assume that gravity is equally strong anywhere on Earth (that’s roughly true, but an assumption that is a valid simplification for a lot of practical geometry), does the location of the slope matter? It could be in Death Valley or on Mount Everest: the ball, having rolled down the slope, will eventually have the same kinetic energy. The probability at the top and bottom of the slope is irrelevant; What is important is the difference in voltage between the top and the bottom. If we assume that the Earth’s gravitational field is the same anywhere we might take this slope, only the height of the slope is relevant.
So, since voltage is a difference, we need 2 points to get voltage. If we say that some node in the circuit is 5V5V, then we say that it is 5V5V more than some other point. The basis is that other point, unless the context states otherwise.
Similar agreement exists with altitude. If you say the height of Mt. Mount Everest has a height of 8848 m, 8848 m, and you will assume that its height is 8848 m above sea level. I can also override this reference with clear context. For example, I can say Mt. Mount Everest is higher than K2 by 237 meters and 237 meters. The default reference can also change. For example, if you say Olympus Mons is 21,229 square meters and 1,229 square metres, you would probably not assume that this is higher than sea level, but there is an equivalent reference on Mars. There is no universal reference f

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