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Volt

The volt (symbol: V) is the unit of electric potential, electric potential difference (voltage), and electromotive force in the International System of Units (SI).[1]

For other uses, see Volt (disambiguation).

volt

SI

electric potential, electromotive force

V

Alessandro Volta

kg⋅m2⋅s−3⋅A−1

Water-flow analogy[edit]

In the water-flow analogy, sometimes used to explain electric circuits by comparing them with water-filled pipes, voltage (difference in electric potential) is likened to difference in water pressure, while current is proportional to the amount of water flowing. A resistor would be a reduced diameter somewhere in the piping or something akin to a radiator offering resistance to flow.


The relationship between voltage and current is defined (in ohmic devices like resistors) by Ohm's law. Ohm's Law is analogous to the Hagen–Poiseuille equation, as both are linear models relating flux and potential in their respective systems.

resting potential: ~75 mV[6]

Nerve cell

Single-cell, rechargeable [7] or NiCd battery: 1.2 V

NiMH

Single-cell, non-rechargeable (e.g., ): alkaline battery: 1.5 V;[8] zinc–carbon battery: 1.56 V if fresh and unused

AAA, AA, C and D cells

: 1.2 V, 1.5 V, 1.8 V, 2.5 V, 3.3 V, 5.0 V

Logic voltage levels

rechargeable battery: 3.3 V

LiFePO4

-based lithium polymer rechargeable battery: 3.75 V (see Comparison of commercial battery types)

Cobalt

/CMOS (TTL) power supply: 5 V

Transistor–transistor logic

: 5 V DC

USB

: 9 V

PP3 battery

systems are 2.1 volts per cell; a "12 V" battery is 6 cells, or 12.6 V; a "24 V" battery is 12 cells, or 25.2 V. Some antique vehicles use "6 V" 3-cell batteries, or 6.3 volts.

Automobile battery

third rail: 600–750 V (see List of railway electrification systems)

Rapid transit

High-speed train overhead power lines: , but see the List of railway electrification systems and 25 kV at 60 Hz for exceptions.

25 kV at 50 Hz

High-voltage lines: 110 kV and up (1.15 MV is the record; the highest active voltage is 1.10 MV[9])

electric power transmission

: a maximum of around 150 MV.[10]

Lightning

The voltage produced by each electrochemical cell in a battery is determined by the chemistry of that cell (see Galvanic cell § Cell voltage). Cells can be combined in series for multiples of that voltage, or additional circuitry added to adjust the voltage to a different level. Mechanical generators can usually be constructed to any voltage in a range of feasibility.


Nominal voltages of familiar sources:

History of the electrical units.