# What is voltage?

I am a little unclear on what voltage actually is and I am trying to find out what the physical cause for voltage is. Is it the speed of the electrons through the conductor or is it an excess of electrons on the supply side of the conductor. I somewhat understand electromagnetic induction in transformers but I can't seem to figure what the voltage is physically.

• en.wikipedia.org/wiki/Voltage sorry Brian, but it's the first port of call..... – user81619 Aug 30 '15 at 18:47
• Voltage is simply a difference in electric charge, caused by a number of things. In a battery voltage is caused by a chemical reaction. In a lightning storm, voltage is created by friction. Essentially any time there are more electrons in one place than another you will get a voltage. – Sponge Bob Aug 30 '15 at 18:47
• I can't believe I'm about to say this, but thanks sponge bob that actually helped a lot lol. I've had a hard time asking this question because didn't know enough to phrase the question right but that did actually help and now I can continue my studying thanks. – Brian2263 Aug 30 '15 at 20:31
• Energy per charge. – DanielSank Nov 9 '15 at 3:24
• Possible duplicates: physics.stackexchange.com/q/55948/2451 and links therein. – Qmechanic Nov 9 '15 at 12:58

Voltage is, at heart, simply a way to quantify the fact that separate electric charges produce a force on each other. Similar charges repel, opposite charges attract. It is seen as a measure of the intensity of an electric field. An electric charge in an electric field will experience a force which tries to move it (an electromotive force), and it is this force which measured by voltage. Admittedly it gets more complicated than that, with distance (for instance) often thrown in, so field strength is not measured in volts, but rather volts per meter, but that's the heart of it.

Since electrons come with nicely discrete and uniform charge, and an electron which moves through a voltage of 1 volt will either require or provide a fixed, uniform amount of energy (since force times distance equals work), in some areas the electron-volt is a convenient unit of energy, but I assume you're not being confused by this.

• Thanks, this also helped me out and gave me a little more detail into this. – Brian2263 Aug 30 '15 at 20:36
• @WhatRoughBeast - I have also been very confused about how distance affects voltage. As you said, voltage is a way of measuring electromotive force, since a force acting on a charge gives it the ability to do work, aka a voltage is created. But work is also proportional to distance, so it seems one could increase voltage by increasing the distance the charge is separated, which would actually decrease the force acting on the charge according to coulmb's law. This makes it seem like voltage is actually a bad way to measure electromotive force. Do you have any answers for me or do you know any – Peter Blood Jul 2 '18 at 5:10
• @WhatRoughBeast - sources I could read up on voltage more in depth, specifically why it is measured as the difference in potential per charge between two points? I've actually asked many questions about this on my handle, but haven't gotten any answers that would reach my point of satisfaction. – Peter Blood Jul 2 '18 at 5:14
• @PeterBlood - Sorry, but you're missing a lot. You've missed the fact that voltage can measure either attraction or repulsion. In your example, if the charge is attractive, you have to do work to increase separation, in order to overcome the force. If the charge is repulsive, work is done by the charges as the distance increases. Your final "why" is, frankly, so basic and so apparently missing the point of the definition that I can't help you. – WhatRoughBeast Jul 2 '18 at 11:58

If you take the hosepipe analogy, the total amount of water flowing through the pipe is charge, the amount per second is current, resistance is resistance and in order to get a flow though the resistance you need pressure. Which is the voltage.

Voltage is potential energy per charge. It's a function of space, so if we move one electron from a place where the potential is 2V (Location A) to where it is 1V (Location B), that takes 1 eV of work (note the sign because electrons are negative).

The reason one place is 2V and the other is 1V is because there is electric field in between, which pushes our electron and is set up by other charges that must exist somewhere. Moving the electron against this field requires the 1eV of work. Also, being potential energy, voltage is relative so we could just as easily assign Location A as 40 V and Location B as 41 V.

A battery holds its terminals at a fixed voltage, no matter what it's connected to/what it's environment is. For example, a 9V battery will always rearrange charge and push the current required to keep its terminals at 9V. That is the nature of the chemical reaction inside the battery.