Physically - Electricity and Volts

[DwithQs]

I apologize for my very basic question, but I cannot find a straight forward answer anywhere. I want to know "Physically, what are volts". I understand that amps are a count of electrons passing a point in one second. I know the formula for Ohm's law, but that still doesn't answer the question in my mind. I've read that a volt is a measurement of pressure, or the measurement of potential difference of charges between two points. Ok, what physically causes that difference? Is it that there are more electrons at point A than at point B and they want to move to point B? If that is the case, then how does the voltage stay the same once some electrons have moved to point B? Also, how is the voltage regulated in a battery. I see that it stays the same at all times. How is that?

 

[Hootenanny]

Before thinking about voltage, you should have a clear idea of what Electric potential energy is (see here: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elepe.html#c1). Potential energy (in general) is a far more fundamental concept than voltage and once you understand it, the definition of voltage will be clearly.

I know that your question relates to circuitry rather than individual electrons, but it is important you understand the basic concepts before moving on.

Information on voltage can be found here: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elevol.html, but I really would recommend reading about Electric Potential Energy first.

 

[rcgldr]

It might help to use an analogy. Voltage is a potential, a potential energy per unit charge. Using gravity as an analogy, for object close enough to the surface of the Earth that gravity can be considered a constant force (or field), then gravitational potential energy = m g h, and gravitational potential = g h.

You could think of voltage as force x distance / (amount of charge on some object in an electrical field). The convention for voltage assumes a positively charged source, and as distance from that source increases, the voltage decreases. The electrical potential energy for some object in an electrical field would be voltage times the charge on the object minus the electrical potential energy of some reference point. For a point source, using a reference of infinite distance from the source is convenient since voltage from a point source is relative to 1/distance, so at infinity it would be zero. For the field between the plates of a capacitor, the reference point is the surface of the positively charged plate and voltage goes linearly to zero at the surface of the negatively charged plate.