LearnTronics
Voltage
What is a volt?
This question trips up many beginners because saying “voltage is electrical pressure” only moves the question one step away.
A volt describes electrical potential difference. More specifically:
A useful first picture: pressure
One letter doing two jobs
V is used both as the usual variable for voltage and as the unit symbol for volts. Context tells us which one is meant.
For example, V = 23 V is read: “the voltage is 23 volts.” The V on the left names the quantity; the V after 23 names the unit.
Voltage is often compared with water pressure. More pressure can push more water through a restriction. In a circuit, more voltage can drive more current through a given resistance.
This is a useful electrician's picture — but voltage is not literally water pressure.
Another way to think of this: height
A ball at the top of a hill has the ability to release energy as it rolls downhill. Electrical potential difference is somewhat like having charge at different electrical “heights.” The greater the difference, the more energy per unit charge is available to be transferred.
What is really happening?
Voltage compares the electric potential at two locations. A source such as a battery uses chemistry to maintain a potential difference between its terminals. When a complete conductive path is connected, that electric field can transfer energy to charges in the circuit.
So voltage does not “flow.” Current flows; voltage is a difference between two points.
Where did the name come from?
The volt is named for Italian scientist Alessandro Volta (1745–1827). Around 1800 he developed the voltaic pile, an early battery capable of producing a continuous electric current.
His name lives on every time we measure a battery as 1.5 V, 9 V, 12 V, 120 V, and so on.
Worked example
Question: A source provides 12 joules of energy to move 2 coulombs of charge. What is the voltage?
Answer: 6 volts.
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A little deeper
Electric potential is measured relative to some reference point. In practical circuits we often call one point ground or 0 volts and describe other points relative to it. That does not mean the Earth itself must always be involved; “ground” is also commonly used as a circuit reference.