# What exactly is a "volt"?

What exactly is a volt? So I Studied the chapter "electricity" in the month of April and got introduced to the concept of "volt".

The concept was too unclear for me so I tried to ask some questions to my teachers and to do some searches on google and watch some videos.

I observerd that noone is giving me a suitable answer. Everyone just gives the analogy of a water bottle with holes in it. I don't think that a circuit is a water bottle.

I didn't want to ask this question on stack exchange but its getting too confusing and I just couldn't grasp it.

What exactly is volt? Is it energy? Because everyone talks about it in a way which makes it look like it is something that affects the flow of electricity.

I need to ask what exactly is something?

• What about e.g. the Wikipedia article is unclear to you? It's the unit of electric potential. Aug 16, 2016 at 13:40
• Just from my experience, and I think a lot of people would agree: it's hard to grasp what the point of having a thing called voltage is when you are new to the idea. I mean, I used to think, "why do people say high voltage instead of high current?" A volt is a difference in energy per unit charge. The only way to understand what it is is to familiarize yourself with it. If you take up higher levels of physics the idea of a volt will become (at the risk of sounding dramatic) part of your soul, and you won't even realize it:) Aug 16, 2016 at 13:45
• Possible duplicate of Could someone intuitively explain to me Ohm's law?
– user121474
Aug 16, 2016 at 13:58
• "I observerd that noone is giving me a suitable answer." have you tried any textbook in physics? Aug 16, 2016 at 21:43
• @JayJay That just means that you've worked with it long enough to have a feel for what different values of voltage mean. It doesn't mean that you've gained an insight into what it is. The only way to really grasp it is to understand the gravity analogy given in an answer below, I think.
– user97626
Aug 16, 2016 at 22:00

There's a close analogy to gravity, perhaps it will help to take a look at it.

I can define a quantity $X=gh$ (near the surface of the earth) where $g$ is the acceleration due to gravity and $h$ is the height above the surface. It's hard to make any intuitive sense out of that quantity. But if I multiply by the mass of an object at that height I find $U=mgh$, energy. So we might say $X$ represents a potential to become energy at that point.

Similarly I can define a quantity $V$. It's hard to make any intuitive sense out of that quantity. But if I multiply by the charge of an object at that position I find $U=qV$, energy. So we might say $V$ represents a potential to become energy at that point.

There's one unfortunate thing to watch out for. The word potential gets used in two different but closely related concepts: electric potential and electric potential energy. Similarly we can have gravitational potential and gravitational potential energy. I know that when I was starting out this caused me some confusion.

I recognize that this is not a direct answer to "What is a volt?", but the volt is an abstract quantity. We define it as a convenient stand-in for energy; it simplifies a lot of analysis. It's not a directly physical quantity like force or distance.

• Why not just giving the definition of potential energy instead of giving an analogy? I never understood how comparing electromagnetism to other things could possibly be easier than just learning electromagnetism. Aug 16, 2016 at 14:03
• @GennaroTedesco I think the OP has been trying to learn electromagnetism, and has reached something that the conventional line of reasoning doesn't explain to him or her. An analogy might help. I readily admit it won't help everyone. The OP is a novice, and doesn't think the same way you or I think. Aug 16, 2016 at 19:46

Let $\mathbf{E}(\mathbf{r})$ be the electric field: the work done by the field on a unitary charge $q$ along the path $\gamma$ is, by definition, $$W_{\gamma} = \int_{\gamma}\textrm{d}\mathbf{r}\cdot\mathbf{E}(\mathbf{r}).$$ If the work done by the field happens not to depend on the path $\gamma$ but only on its boundaries instead, we say the field is conservative and express the associated work done as difference of a function calculated on the boundaries, namely $$W_{\gamma} = V(A) - V(B) = \int_{\gamma}\textrm{d}\mathbf{r}\cdot\mathbf{E}_{\textrm{cons}}(\mathbf{r})$$ for conservative fields $\mathbf{E}_{\textrm{cons}}(\mathbf{r})$. Calculating the above along any path $\gamma$ walking by any point in space one defines the function $V(x)$, referred to as the potential energy of the field.

Let us take the particular case of a conservative constant electric field. The associated work done along a path $\gamma$ is therefore expressed by the difference of potential $$V(A) - V(B) = |\textrm{E}|\,\Delta r.$$ We call difference of potential of 1 Volt the work done by the above field of module 1 N/C$to move a unitary charge of 1 m. Volts or voltage is the amount of potential energy that electrons have relative to another point, usually what's called "ground", which is defined as having a potential of 0 volts. In some devices, this is related to current by what's called resistance (measured in ohms), which is the ratio of voltage to current in said device. Specifically, voltage is the amount of energy per coulomb of charge, so volts have the dimension of Joules per Coulomb. If you want a real-world analogy, one decent (not the best, but decent) comparison I like to use is the analogy of water in pipes. Current is literally just the amount of water flowing through the pipe. More water means more water molecules flowing, which is analogous to electricity flowing through a wire. Voltage, on the other hand, can be thought about in terms of falling water: water which falls from a high waterfall has more potential energy than water which falls over, say, the edge of a small rock at the base of the waterfall. Here, again, we measure potential relative to the ground. So a volt is the "pressure" In the wire. The more the volts the more potential for movement. So if you increase the voltage of something than the current or speed of energy movement increases because moreveryone energy is going through the same wire. Bob has a voltage controller and the harder he presses the button the more volts flow through the circuit into the lightbulb. At first he presses down gently and the bulb is lit dimly. Eventually he presses harder and since there are more volts in the wire the current is moving faster so the bulb gets brighter. He then stops pressing and since there are no volts going through the circut, there is no pressure, the light goes out. He then slams the button with a hammer and so many volts go though the circus that the wires are overcharged. Like if you hook up a huge water pump to a tiny pipe the pipe will break because the water pressure is too high. Another analogy you could use (this one actually makes sense) Voltage (V) is the potential for energy to move and is equivalent to water pressure. Current (I) is a rate of flow and is measured in amps. Ohms (r) is a measure of resistance and is equivalent to the water pipe size. These three terms are related to each other with a simple formula that reads, current is equal to the voltage divided by the resistance. I=V/r Imagine you have a tank of water with a hose connected to the bottom of this tank.. What happens if you increase the pressure inside of this tank? The amount of water flowing out of the hose will also increase. The same is true when you increase voltage, more current will flow. What happens if you connect a larger diameter hose to this tank? The flow rate will also increase because the resistance dropped. The same is true if you use a large gauge wire when moving current. The larger the wire the more current you can move through it with damaging the wire. I hope this makes sense, good luck on the test ;) By definition, a volt is a joule per coloumb: $$V \equiv \frac{J}{C}$$ This arises from the definition of electric potential: the amount of potential energy per unit charge in a circuit or system. To give an analogy, electric potential is to electricity as height/distance (essentially gravitational potential) is to gravity. Electric potential difference, more commonly known as voltage$\Delta V$, determines the current$I$in a circuit given some resistance$R$. This is known as Ohm's law and is given by the equation$\Delta V = IR$. Many people say it is "electrical pressure" but I don't personally like that analogy. I prefer the analogy to gravity. Think about a ball rolling down a hill. Why does it not roll up the hill? The ball moves to minimize its potential energy, being accelerated by Earth's conservative gravitational force. The bottom of the hill is closest to the center of the Earth, the lowest possible height, and therefore the lowest gravitational potential. Similarly this is true of electric charges. The lowest electric potential is the location of minimal potential energy for positive charges*, and particles in a conservative field move to the location of lowest potential energy. While moving to that position, you have current in accordance with Ohm's law. *For negative charges, the lowest potential energy is at the highest electric potential. Electrons move in the direction of increasing electric potential. • "The ball wants to be in its lowest energy state" - ugh... Aug 17, 2016 at 2:14 • @AlfredCentauri Care to elaborate? I want to be more accurate if you can to provide more feedback -- "ugh" isn't very helpful. I could instead say that the "ball moves to minimize its potential energy, i.e. towards the ground state, where it is most stable." It's a difficult point to phrase, not to mention my "artistic" use of personification. – zh1 Aug 17, 2016 at 2:26 • zhutchens1, do I really need to elaborate? Is the best answer, at the level of serious students of physics, to the question "Why does it [the ball] not roll up the hill" really that the 'the ball doesn't want to'? From your comment, I see that you probably don't think so. Act in accordance with that. Aug 17, 2016 at 2:59 • @AlfredCentauri Thanks. I edited my answer to be a bit more precise. Though I might contend that a "serious student of physics" will find the definition of electric potential and its units to be basic/fundamental knowledge. – zh1 Aug 17, 2016 at 3:21 Here we have a bunch of positively charged particles (colored black) and negatively charged particles (colored white): Now suppose we drop in a negatively charged particle at point A. It's going to try to move left, because it's attracted by all those positive charges on the left and repelled by the negative charges on the right. (There's also a negative charge on the left, but that's more than balanced out by all the positives.) Suppose you want to move that particle from point A to point B. Then you're going to have to push against all that electrical force, so it will take some energy to move that charge from A to B. The voltage between points A and B is the amount of energy you'll need for that --- that is, the amount of energy it takes to move your negative charge from A to B, overcoming the electrical forces along the way. Suppose that voltage happens to be, say, 3. One way to express that is to say that the voltage at A is 1 and the voltage at B is 4. Or you can say that the voltage at A is 6 and the voltage at B is 9. Or that the voltage at A is$-2$and the voltage at B is$+1$. You can pick a perfectly arbitrary number to assign to point$A$, as long as you assign that number plus 3 to point$B$. So let's go ahead and say (arbitrarily) that the voltage at$A$is$2$and the voltage at$B$is$5$. Again, all we mean by this is that it takes 3 units of energy to move one unit of charge from$A$to$B$. Now suppose there's another point$C$, and suppose it takes 7 units of energy to move a unit of charge from$A$to$C$. That is, the voltage from$A$to$C$is$7$. Then since we already decided to call the voltage$2$at point$A$, we have to call it$9$at point$C$. Now: How much energy does it take to move a unit of charge from$B$to$C$? Well, the number we assigned to$B$--- the voltage at$B$--- is$5$. And the voltage at$C$is$9$. Therefore, we predict that it will take$9-5=4$units of energy to move a unit of charge from$B$to$C$. And it turns out, empirically, that if you make predictions this way, you're always right. So in summary: The voltage between$A$and$B$is the energy needed to move a unit charge from$A$to$B$. The voltage at$A$is any number you care to make up --- you can call it$2$or$-100$or$3.14159$. Once you've made that number up, the voltage at$B$or$C$or$D$, minus the voltage at$A$, is the energy needed to move a unit charge from$A$to$B$or$C$or$D$. And---miraculously---once you assign numbers this way, you can also use them to figure out how much energy it takes to move a unit charge from$B$to$C$or from$B$to$D$or from$D$to$C$, just by taking differences. If you don't like the pressure analogy, I guess you wouldn't like this illustration: Could someone intuitively explain to me Ohm's law?. But it's worth a try to have a look. Apart from that, voltage$V$(with the unit of volts$\mathrm V\$) is just energy per charge; meaning Joules per Coulomb:

$$\mathrm{[V]=\left[\frac JC\right]}$$

In other words, the voltage is the amount of energy (potential electrical energy, as it's called) stored at a point in the circuit per unit of charge.

If one point in the circuit stores more of this energy than another, then the charges will move towards the other point. Charge will always want to be at a spot with the lowest possible energy.

• Just like a spring, that can store energy when stretched, which will always try to return to it's unstretched (lowest-energy) shape.

And this is why people use the "water pressure" analogy. Because the difference in energy between two points is what makes the charge move from one point to the other - as if there is a larger "pressure" on them at one point "pushing" them to the other point.

## In more depth

The reason is that potential electric energy is "stored" when more charges (of the same sign) are gathered.

• One electron alone causes no potential energy,
• but add two electrons to the same point in the circuit, and they will repel each other. Like a spring that is compressed. If you let them go, they will move away from each other.

This "stored energy" arises from the fact that they are repelling each other and have nearby spots in the circuit where they are repelled less from - so they will naturally move there. This will reduce the potential energy of this system - reaching a configuration of lowest energy is of this reason the goal for any potential energy system.

So, all in all the volt is simply the energy per charge at a point, and it can be compared with other points in the circuit so we know if charge wants to move there or not.

• Please notice that the concept of voltage is independent on the concept of circuit and current flowing through a circuit. Aug 17, 2016 at 8:05

An electromagnetic field is an area in space that has a certain potential. What potential? It has the potential to uplift an electron and in that process, it gives a spin to the electron so that it can move. Whether an electron will actually move into that space does not happen by itself. But when we 'generate' electricity using magnets, it is this electromagnetic space that first moves... and in the process uplifts electrons and gives it a spin... Once in motion... it has a tendency to keep on moving... but faces resistance due to many factors including the attraction to positive charges on the way and comes to a stop at a certain point.. At that point, if there is any further energy left in the electron, it releases the energy either as heat or electromagnetic radiation.

Voltage is the amount of energy required to move the charged element from one point to another. Voltage between point A and Point B could be 3 volts... But the Voltage between Point A and Point C could be 9 volts... And this is because every point has a potential to suck/store/release electromagnetic charge/energy... The difference in potential is called as voltage. Conversely, the amount of energy required to move a charged element from one point to another is also voltage. Both are same.

The earth being a huge positive, it simply has an ability to attract all electrons and suck it all up unless there is electrical insulation. Hence it is also called ground/negative.