CoachThe voltage between two points of a circuit measures the electrical push available between them — how hard the current is driven from one point to the other, as a waterfall’s height measures how hard it drives the millwheel. Voltage is always a between: between the two terminals of a battery, between the two sides of a lamp — never at a single point alone. Its unit is the volt (), honoring the inventor of the first battery.
Examples
Example 56.2 (The volt family album)
A single round cell: . The flat pocket battery: — three cells nose-to-tail inside one wrapper. The rectangular nine-volt with both terminals on top: , six hidden cells. A car battery: . The wall socket: — more than a hundred and fifty little cells’ worth of push, which is the whole quantitative content of “the socket, never”. Lightning between cloud and ground: hundreds of millions of volts, briefly.
Example 56.10 (The open switch’s confession)
Lamp dark, switch open — where did the push go? Measure: across the dark lamp, ; across the open switch, the full . The battery’s push stands entire across the gap, waiting — the one place in the loop where two points are truly “far apart” electrically. Close the switch and the readings trade places. An open switch is where the voltage waits.