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I apologize if this is a stupid question, but I cannot find any answers online, so I feel I must ask here.

I do not quite understand exactly what voltage is. I see on batteries, "X Volts", but I do not quite know what that means. I looked online and read sources on volts, amperes, and watts, and it has only confused me more. What exactly is voltage? If it isn't a measure of the electric current, then why is it used on batteries as a measure of their electric power? Why aren't amperes used?

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  • \$\begingroup\$ voltage is potential energy per charge carrier. \$\endgroup\$
    – MarkU
    Jan 15, 2016 at 21:01
  • \$\begingroup\$ current is the rate at which the charge carriers flow. so voltage x current is the rate at which energy flows, also called power. \$\endgroup\$
    – MarkU
    Jan 15, 2016 at 21:08
  • \$\begingroup\$ .. and also electronics.stackexchange.com/questions/6312/… \$\endgroup\$
    – pjc50
    Jan 15, 2016 at 21:08
  • \$\begingroup\$ Charges move due to force exerted upon them. Usually the charges are electrons. Voltage is a measure of the strength of the force acting on the electrons. Current is a measure of how many charges (electrons) move past a point in a given time period. When a battery is just sitting on a shelf, there is no current flowing through it. So measuring current would not be very helpful. \$\endgroup\$
    – mkeith
    Jan 15, 2016 at 21:15
  • \$\begingroup\$ As a very simple explanation I personally like this picture: paulhunt73.webspace.virginmedia.com/mgb-stuff/images/… \$\endgroup\$
    – Steve G
    Jan 15, 2016 at 21:20

3 Answers 3

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The technical definition of voltage is energy (joules) applied to charge (coulombs). This energy allows the charges to flow through resistances and to energize inductances.

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We often use a water analogy to explain electric circuits. It's not very good but it can help.

schematic

simulate this circuit – Schematic created using CircuitLab

  • The battery is like a pump that tries to generate constant pressure. Symbol: \$V\$ measured in volts.
  • The electrical current is like the water flowing around the circuit. Symbol: \$I\$ measured in amps.
  • The pump experiences resistance in the circuit. This includes the pipes, the radiators, valves, etc., which all resist current flow. Symbol: \$R\$ measured in ohms, 'Ω'.

Effects

  • The higher the pump pressure (voltage), the more water will flow.
  • The higher the resistance the less water will flow.
  • If we double the resistance and keep the voltage the same only half teh current will flow. The pressure (voltage) at the mid-point will be half that at the pump (battery).

You can work out the current in each circuit from Ohm's Law, \$V = I \cdot R\$.

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Voltage is a measure of electromotive force (emf) or potential energy per unit charge. It's not really a force, not is it energy - but you can think of it as the 'force' or 'pressure' of the electricity.

What is it exactly? Nobody knows. What we do know is that opposite charges attract and like charges repel. Inside an atom the electrons (which each have 1 electron unit of negative charge) are attracted to the protons (which have 1 unit of positive charge). Chemical reactions in the battery force electrons towards the negative terminal. The electrons are still attracted to the protons, but they can't get back to them unless an external path is provided to the positive terminal.

The closer the electrons are to the protons in the atom, the more energy is required to remove them. This is the potential energy per unit charge. Current is the number of electrons that flow past a particular point in an electric circuit. Power is voltage multiplied by current, which is the rate of energy transfer from one place (or form) to another.

Voltage by itself is not power, but words are often used ambiguously. 120V AC is called mains 'power' because it provides power when current is drawn from it. AC is short for Alternating Current, even though no current has to flow for an AC voltage to be present.

The power you can get out of a battery is determined by both its voltage and the maximum current that it can deliver. But why only mark the battery with its voltage? Higher voltage can force more current through a circuit, and most devices are designed to work at a particular voltage. A battery with higher capacity (Ampere-hours or Watt-hours) can run a device for longer, but higher voltage could blow it up.

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