# What is a Charge?

I'm a high school student. I love computers and electronics. Few weeks ago, I thought to build my own electronic gadget but, unfortunately I had not much knowledge in electronics. So, I decided to learn. After Googling here and there, I came across a large amount of information. Nothing, except one thing, that daunts and intimidates me is that what the term Charge means? None of the books tell what it means. Some tell that it is the basic property of the matter and just it and don't define further about it. Whereas some don't even bother to tell about it. On Wikipedia it is defined as:

Electric charge is the physical property of matter that causes it to experience a force when close to other electrically charged matter.

The definition is quite bit difficult and confusing. Similarly from All About Circuits Website tutorials I got a different type of definition and understanding.

From books, I came to know that we still don't know much about charges even great scientists like Sir Stephen Hawking doesn't known much about it. Is it correct? If not, then why was it written in the books (I mean here books not a book), what is its correct definition? Why majority of books don't define what charges is/are?

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Would it help if I told you that current is a flow of charge? Electric current –  Andrew Morton Mar 19 '14 at 19:10
Some tell that it is the basic property of the matter and just it and don't define further about it. Which is as it should be. If one could explain a basic property of matter in 'more' basic terms, it wouldn't be a basic property of matter. If you think very carefully about this, you'll realize that, at some point, we discover what we believe are fundamental properties, i.e, properties that cannot be explained in terms of other 'more' fundamental 'stuff'. Electric charge is, we believe, one of those fundamental properties. –  Alfred Centauri Mar 20 '14 at 2:33
If understanding charge is defined as: 'we know how to manipulate it so well that we can use it for our own purposes', then we understand charge very well. As I pointed out in my answer to this question, there is no question to which you can not respond 'but why is it so'. In that sense, we understand nothing about anything :). –  Chris Mueller Mar 20 '14 at 2:35
It is like asking what is time? –  Awesome Mar 23 '14 at 16:06

Like Ali said, charge is a property (or characteristic or feature) of a particle. The particle could be an atom, or it could just be a part of an atom like an electron or a proton.

Unfortunately, we can't really say much about why particles have this property, or what causes this property to exist. We can only describe some things we observe about this property that we call charge.

• Charge comes in two types, which we arbitrarily label as "positive" and "negative".

• Positive charges repel each other with a force that we can measure, negative charges repel each other similarly, and opposite charges attract each other.

• We find that there are components of atoms called "protons" and "electrons" that are always positively and negatively charged, respectively.

• Charge is conserved. That means, in all the experiments we have tried, the difference between the amount of positive and negative charge in a closed system is the same at the end of the experiment as it was at the beginning of the experiment, and we therefore believe this is true of all closed systems in the universe.

Even though we don't know what charge is or where it originally comes from, the description of what it does is enough for us to predict lots of useful things and make lots of useful tools like radios and computers.

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You really wrote an awesome piece of text.... Nice to meet you... Thank you very much! –  seek_learn_joy Mar 22 '14 at 18:44

To keep it simple for now (once you get to college physics this will be expanded), charge is electrons piled up, or lack of electrons where you'd expect there to be some. Electrons have negative charge and protons positive charge. A normal atom has the same number of electrons as protons, so no net charge.

On some atoms, the outer few electrons are somewhat "loose". When you have a whole bunch of these atoms all next to each other, like copper atoms in a copper wire, these loose electrons can jump around between adjacent atoms. However, if they jump too far, they leave a positive charge (since a negative one went away) where they left, and a negative charge where they are. This imbalance of charges creates a electric field, which you can think of as a force field that pushes and pulls on electrons. Electrons are pulled toward to positive charges and pushed away by negative ones. This electric field therefore won't let the electrons vacate one location and pile up in another over the space of a few atoms.

A voltage source, like a battery, is something that creates a electric field. If you connect opposite ends of the battery to opposite ends of this copper wire with all the somewhat mobile electrons in it, you can get all the electrons on average to move from the negative voltage end of the wire to the positive voltage end. To keep maintaining the electric field applied to the wire, the battery then pumps the electrons that flow off the + end of the wire back onto the - end of the wire, where they again hop between copper atoms and end up at the + end again.

The mass movement of electrons is called current, which is charges flowing. This is a lot like current in a river is lots of little water molecules flowing. Since the charge of one electron is very very tiny and of little use at our human scale, we use a unit of charge called the Coulomb. However, a Coulomb is just a calibrated pile of charge. In fact, it's about 6.24 x 1018 electron charges worth. Actually it's -6.24 x 1018 electrons since we arbitrarily decided electrons have negative charge.

Again to keep the range of numbers nicer on a human scale, we measure current in Amperes, which is one Coulomb of charge flowing by every second. So if you have 1 Ampere (sometimes "Amp" or the official abbreviation "A") flowing left to right in a wire, then there are actually 6,240,000,000,000,000,000 electrons flowing right to left per second past any one point along that wire.

Now that you have a basic idea what charge and current are, forget about electrons moving with their negative charges. The rest of electronics is all built on Amp and Coulombs. Think of that as the conceptual units of current and charge you'll be using from here on. The fact that these happen to (usually) be based on actual negative charges is irrelevant and just invites confusion.

So now let's go back to that battery that caused current in our wire. A battery is really just a pump for charge. In other words, it can make current. However, there is one more metric that is important to mention here, which is how hard the battery can push. One battery may be able to push harder on charges than another, just like one water pump can make a higher pressure than another. It is this pressure that makes the electric field that makes charges move, which is current. This electric pressure is measured in units of Volts. The more Volts a battery can make, the more current it can cause to flow thru the same resistance. This is just like a higher pressure water pump can make more water flow thru the same size nozzle.

So how can we related voltage, current, and resistance? As you can probably see more voltage (pressure) makes more current (flow), but more resistance (smaller nozzle) makes less flow. To put this mathematically:

current = voltage / resistance

This also gives us a definition of resistance by rearranging this equation:

resistance = voltage / current

The concept of resistance comes up a lot in electronics, so we have a special unit just for measuring it, called the Ohm. In fact, the Ohm is defined as:

Ohm = Volt / Ampere

We have short abbreviations for all three of these quantities since just about all of electronics is based on them. A Volt is abbreviated "V", the Ampere as "A", and the Ohm with the greek letter "Ω".

This equation that relates resistance, voltage, and current is a cornerstone of electronics, and is called Ohm's Law, after the guy who first came up with it.

Let's go back to the first form of Ohm's law I showed, which tells us how much current we get:

In physical quantities: current = voltage / resitance
In common units: Amps = Volts / Ohms, or A = V/Ω

That's a great deal to think about already. Try to wrap your mind around this before going any further. Ask questions here as you need to to understand this. Once you get this, we can go on to all kinds of cool stuff.

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Very good explanation. Now, who said that professionals can't write schoolbooks? :) –  Dzarda Mar 19 '14 at 20:30
What utterly infuriates me is that this explanation isn't used more widely; it seems like a lot of folks who teach or write about this stuff are hell-bent on avoiding any analogy, no matter how applicable, on the misguided notion that it somehow 'contaminates' the technical purity of their own personal understanding of the matter. +1 for giving a clear English description of a simple set of mechanics. –  user39062 Mar 21 '14 at 18:47
To give you a sense of the scale of the numbers used when dealing with the individual atoms, there are 1.08e25 atoms in 1kg or iron. If that mass was holding a charge of 1C, or 6.24e18 more electrons, then roughly 1 in two million atoms would actually have an extra electron. If you consider that each iron atom has 26 elections "normally", that bumps it up to 1 in 50 million electrons being "extra". –  Yos233 Mar 22 '14 at 9:02
why do electrons get pulled to positive charge? –  Dude Bro Mar 23 '14 at 16:58
@Dude: They just do. This is one of those fundamental physical properties that we don't know how to decompose into more detailed explanations. We have found that like charges repell and opposite charges attract. We have quantified this with equations, and found those equations to correctly model what we observe in all cases tested so far. We therefore believe this to be a fundamental law of nature. We have built many complex devices that rely on this this law. The fact that they work as expected means we've got something right. –  Olin Lathrop Mar 23 '14 at 17:19

Olin's answer is excellent. I would add to it that an analogy might help.

(For the purposes of this analogy let's ignore everything after Newton. General Relativity and the Higgs Boson are interesting but aren't going to help understand charge.)

You probably have an instinctive understanding of mass, specifically gravitational mass. But what is it?

Gravitational mass is a property of matter that causes it to experience a force -- called gravity -- when close to other matter with mass. The individual amount of mass of an atom is very, very small, but we have a lot of them and they can add up to make very large masses indeed.

Though all atoms have a tiny amount of mass, some have much more than others. If you have a bag of hydrogen and a bag of lead with the same number of atoms in each, one will be much more massive than the other.

A numeric description of how a massive object affects another is called the gravitational field. If you imagine a large mass -- the Earth, say -- and imagine a tiny mass -- a ball bearing, say -- magically suspended at a point above the Earth, if you suddenly magically let it move, it would move in a particular direction -- towards the center of the Earth. Imagine the Earth surrounded by a field of tiny arrows, all pointing in the direction that ball bearing would fall. The length of the arrow is how hard the ball bearing would be pulled: very hard near the surface of the earth, hardly at all past the orbit of the Moon. That "field" of arrows is the gravitational field of the Earth.

Charge is very similar to gravitational mass. Like mass, it is a fundamental property of matter. Like mass, it causes two objects to experience a force between them. Like mass, just as some kinds of matter are more massive than others, so too some kinds of matter are more inclined to produce charge than others. Like mass, you can take a large source of charge and imagine a field of arrows around it that tell you in what direction and how strong the force would be on a small charge placed there; that's the electrostatic field.

How then are charge and mass dissimilar? The major differences between charge and mass are:

(1) Mass only comes in one kind, charge comes in two kinds. All mass is attracted to all other mass. Like charges repel, unlike charges attract.

(2) The charge forces are enormously larger than the gravitational forces. Rub a balloon on your hair and stick it to the ceiling. The charge forces in that balloon are enough to overcome the attraction of an object the size of the Earth! (Though admittedly, distances are relevant. Your balloon is thousands of meters away from the center of the Earth and very close to the ceiling.) The force between masses is absurdly small compared to the force between charges.

(3) Charge is extremely easy to move around compared to mass. The movement of charge through a conductor is a significant fraction of the speed of light. (The movement of individual charged particles can be slow; think of it like turning on a faucet connected to a very long hose already full of water. The pressure wave that spurts water out the business end of the hose travels much faster down the hose than the water coming out of the faucet does.)

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Your way of teaching is nice and I have grasped your concept. –  seek_learn_joy Mar 22 '14 at 18:45
–  Phil Frost Nov 24 '14 at 13:17
Also, the movement of charge through a conductor is very slow. What moves fast is the force, not the charge. Even though you somewhat explain that, you state it first with the wrong words. Misleading. –  Phil Frost Nov 24 '14 at 13:20
I also don't see how charge is easier to move around than mass. In fact, moving charges very fast is very hard. Moving some charge around an ordinary circuit is no more magical than say, tapping a rod at one end with a hammer to transmit a force to the other end of the rod. Not especially hard or magical. It wasn't that long ago that factories were powered by mechanical circuits, analogous to the electrical circuits that run them today. –  Phil Frost Nov 24 '14 at 13:28

Electric charge is the physical property of matter that causes it to experience a force when close to other electrically charged matter.

Sounds like a pretty good definition to me. To quote Richard Feynman:

"We cannot define anything precisely! If we attempt to, we get into that paralysis of thought that comes to philosophers, who sit opposite each other, one saying to the other, 'You don't know what you are talking about!' The second one says 'What do you mean by know? What do you mean by talking? What do you mean by you?', and so on. "

More seriously though; in classical physics there are two important forces. The gravitational force you are probably pretty familiar with. It is the reason why the sun orbits in the galaxy, the reason why the Earth orbits the sun, and the reason why people in China don't fall off of the Earth. You can calculate the gravitational force between two objects using $$F_{grav}=G\frac{m_1m_2}{r^2},$$ where $G$ is a constant $m_1$, and $m_2$ are the mass of the two bodies, and $r$ is the distance between them. The electric force you are probably less familiar with, but it turns out to be the reason that we can see, the reason we have a sense of touch, and the reason that we can build iPhones. For two objects which have charge, such as electrons, you can calculate the force between them with $$F_{elec}=C\frac{q_1q_2}{r^2}$$ where $C$ is a constant, $q_1$ and $q_2$ are the charge of the objects and $r$ is the distance between them.

See the symmetry there! Charge is to the electric force what mass is to the gravitational force! There are some assymetries such as the fact that charge comes in both plus and minus flavors while mass can only be positive, but don't worry about that for now.

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one thing, that daunts and intimidates me is that what the term Charge means?

First a bit of background...

Currently, we believe that, given the observations and experimental results so far, there are four "fundamental interactions" and the electromagnetic interaction is one of those four.

What is a fundamental interaction? From the linked Wikipedia article:

Fundamental interactions, also called fundamental forces or interactive forces, are modeled in fundamental physics as patterns of relations in physical systems, evolving over time, that appear not reducible to relations among entities more basic.

Imagine that you observe that two objects attract or repel each other but that said objects do not attract or repel other objects. In an attempt to explain or model this, you might hypothesize that the two interacting objects have a property that the other objects do not. You might even call this property a charge. You might further hypothesize, after additional observations, that there are two types and that "opposite charges attract" and "like charges repel".

In some cases, the interaction may be explainable by other known phenomenon or, it may be that we determine the interaction simply is - it is the given and the best we can do is model the interaction without being to explain it in terms of something 'more fundamental' .

This is what we do with electric charge and the electromagnetic interaction. We observe it and attempt to model it mathematically and use notions such as electric charge and electric field etc.

At some point, we may discover another, more fundamental 'layer' to reality and be able to answer the question "what is electric charge?" in those terms.

For example, some theorists imagine that electric charge is actually a vibrational mode of a fundamental 1D entity - a supersymmetric superstring - that somehow 'lives' in 10 or 11 dimensions of which 3 are our 'ordinary' spatial dimensions.

But this really only leads to the question "but what is this more fundamental stuff?" What is a supersymmetric superstring?

At this point, it's best not to wonder what electric charge is but, rather, to wonder how it works, e.g., Coulomb's Law.

Further, if you're interested in learning practical electronics, you'll really need to concentrate on circuit theory which is more concerned with voltage and current rather than electric charge.

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Friend, I really like your help for me. You explained in very detail and I like it very much....! –  seek_learn_joy Mar 22 '14 at 18:35

I find it helpful to think of charge as a thing, along the lines of "one electron equals one piece of charge". I don't think that many concepts in electronics correspond directly to the concept of a physical object like this.

If charge is a thing, then 'voltage' describes the amount of energy associated with a particular charge (perhaps analogously to how some object might be hot or cold) and 'current' is the amount of charge that flows through a wire in a given time. The voltage on a capacitor is proportional to the amount of charge stored on its plates, where the proportionality constant is the size of the capacitor. And so on.

That's hugely simplistic, but you might find it a useful mental model to get started with.

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Electric charge is a property, not a thing. An elementary particle such as an electron has the property of electric charge but you cannot find electric charge in isolation, i.e., electric charge is necessarily carried by a particle thus the phrase, "charge carrier". –  Alfred Centauri Mar 21 '14 at 2:11
Yes, I completely agree. I did say thinking of charge as a thing was 'hugely simplistic'. The trick only works because of the fixed relationship: an electron always carries 1.6x10^19 coulombs of charge. I suppose another analogy might be to think of charge as a property of a charged particle in the same way that mass is a property of matter. –  J Ashley Mar 21 '14 at 8:09

To add to Olin's mental picture.

Think of the battery or power supply as something that can take electrons from one side and pile them up on the other so you have a starvation on one end of the circuit and an excess on the other. The starved side then starts pulling those loose electrons off the atoms on that end of the circuit, causing a ripple or chain effect. like a bucket brigade the loose electrons hop from atom to atom toward the starved side of the battery, and as you can guess when you follow that circuit all the way around to the other end of the battery where the atoms have too many electrons they are happy to give them out to the atoms in the circuit who then pass them around. the more the battery can starve one end and surplus the other the faster the atoms in the circuit try to compensate by moving those spares around the circuit. The flow of these spares around the circuit is current. The battery having a surplus on one end and starvation on the other is voltage.

Now how does the battery starve one end of electrons and give them to the other? Well that is the magic of batteries and a separate question. Sometimes it is a chemistry thing, a side effect of chemical reactions. But it depends on the battery technology. Likewise what if it isnt a battery lets say but a wall wart instead or AC coming out of the wall socket? Another good question.

I find it most easy to think of the flow of electrons as you would think of water in pipes, something you can visualize because you have most likely experienced pipes or hoses and water. Water is pumped from one end of the battery to the other, pushing it through the pipe (circuit) and landing in the starved end of the pump, to be pushed through again. We lose a little bit of water in the process so over time the pump just doesnt have enough water to make the thing work anymore (the battery is used up). Resistors are just kinks in the circuit that slow the water down. bigger wires are like a bigger pipe you can move more water through. The speed of the water is the current, hmmm...and so on.

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The most precise answer would be "nobody knows". However, we can still study its properties.

We can model the whole world in terms of 'fields'. A field is like a stretched-out rubber sheet. The sheet doesn't have to be flat; in some places it may rise up and in other places it may dip down. These deviations act like charge. Of course, the real world is 3D but a sheet is only a 2D model.

There are different kinds of fields, based on the way their charge can behave.

There is a field where charge can only go 'one way', for example the sheet might only have upwards bumps, not downwards dips. We call this field gravity, and this 'one way' charge is called mass. Two masses (bumps) will always attract each other, but mass is quite feeble: the bumps aren't very high. This is why a tiny rocket engine is capable of moving away from the Earth, overpowering the mass of the whole planet. However, since all of the bumps go the same way, they will always build up, which results in huge structures like galaxies. The only reason everything hasn't attracted into one huge lump is because the Universe is expanding, which spreads everything out faster than gravity can clump it together.

There is a different field where charge can go 'two ways', for example upwards bumps and downwards dips. This is the electromagnetic field, which electronics is based on. The charge in this field is called 'electric charge', or just 'charge', and we distinguish between the two 'directions' by calling one 'positive' and the other 'negative'. These charges are stronger than mass, which we can see if we use a charged rod to pick up bits of paper. However, unlike mass, like charges will repel each other (positive-positive or negative-negative), and opposite charges will attract. This causes electric charge to get mixed together, like mixing white paint with black paint, so that the result is 'neutral' and it doesn't have much effect on very large (galactic) scales. However, quantum physics stops everything from mixing completely; when we look close enough, there are small, indivisible lumps of positive and negative charge. These are usually electrons and protons, but they're mixed together in little neutral lumps called atoms. Electronics is all about moving electrons around between atoms (note that pulling an electron away from an atom is not the same as 'splitting the atom', which means something else!).

There is another kind of field where the charge can go in three 'directions'. This is called the (strong) nuclear field and behaves in very strange ways. The charge of this field is known as 'colour', with the 'directions' called 'red', 'green' and 'blue'. Note that these are just made-up names, like 'positive' and 'negative', to make sure everyone is talking about the same thing. The words themselves don't mean anything.

If we imagine these fields as rubber sheets, we can stack them on top of each other. There will be patterns in the charge: the bump usually line up, so that, for example, an electric charge moves around with a mass. We call these patterns 'fermions', and give some names like 'electrons', 'pions', etc.

We can also make waves on the sheets. Waves on the electromagnetic sheet correspond to light waves.

Another field is usually mentioned, called the 'weak nuclear' field, but the recent Higgs boson discovery shows that this may actually be part of the electromagnetic field (a theory known as the 'electroweak' field).

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Here's a related explanation of electrical phenomena and how they're difficult to explain in terms of other things by Richard Feynman youtube.com/watch?v=qhh32JYkQPk –  Warbo Mar 24 '14 at 13:10

A charge is a property that some of the elementary particles have. Such as the electron (which has a negative charge) and the proton (which has a positive charge).

Charges are measured in coulomb (read KOOLON) after a French scientist. The electron has -1.6*10^-19 C (negative charge) and the proton has a +1.6*10^19 C.

Charges (or particles that have these charges) of opposite polarities attract and those with same polarities repel each-other. Asking "why" at this level is like asking why the universe exists so things will get philosophical from here. It's just the way the universe works. So yeah... We don't know why a charge exists or how... or what it is exactly. We just call it a "property". And we only describe what it does or how it behaves. Note that we could've arbitrarily flipped the polarities of the charges (an electron would carry a positive charge and a proton would carry a negative one) and everything will still work as before. Because it's still a valid description.

Charge is not a property of the atom. Atoms (in their non-ionized state) are all neutral (they have no net charge : number of electrons == number of protons) Now if somehow an atom loses an electron, the number of positive charges (from protons) will be higher than the number of negative charges so it appears that the atom (now called an Ion/been ionized) carries a positive charge !

A current is a flow of charges. Some examples of that would be :

The flow of electrons in a metal (negative charges) is what you measure as a current in a copper wire.

The flow of ions (the aforementioned ionized atoms) is what constitutes the current in electrolytic solutions.

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-1 for mispronouncing "coulomb". SI units are not capitalized when written out ("in coulomb" instead of "in Coulomb"). The flow of charge doesn't cause current, it is the definition of current. You say that atoms "have no net charge" and then talk about ions, which do have a net charge. –  Joe Hass Mar 19 '14 at 20:51
@JoeHass Sorry didn't know about that "capitalization"... will edit. Corrected. Yeah I meant atoms in their "non-ionized" state then explained. I think it's quite clear. –  br4him Mar 19 '14 at 23:17
And "coulomb" is indeed pronounced like that. It's a French name. I wonder how have you been pronouncing it Mr. @JoeHass ? –  br4him Mar 19 '14 at 23:19
As this is an English language forum, I have been using the normal English pronunciation for the SI unit of charge. The pronunciation of a proper noun in French is another matter, and not really the subject of this discussion. –  Joe Hass Mar 20 '14 at 0:07
Sigh. I don't mean to be offensive, but the page you cited shows four accepted English pronunciations. Two have the emphasis on the first syllable and two have the emphasis on the second. Two use a short 'o' sound in the second syllable and two have a long 'o' sound. However, all of the English pronunciations end with an M sound rather than the N sound that you suggested. –  Joe Hass Mar 20 '14 at 14:22

Say you have a particle, or a group of particles. Create a closed Gaussian surface around it. Then charge can be defined as the surface integral of the electric field flux through the Gaussian surface divided by the permittivity constant. I know this isn't what you were looking for (it's clearly going to be over your head) but I thought it might be a good addition to the other answers here that do answer your question.

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Flux - of what? –  Alfred Centauri Mar 21 '14 at 1:55
@AlfredCentauri Corrected. –  dfg Mar 22 '14 at 18:08

## protected by Olin LathropMar 21 '14 at 15:05

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