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What Is Voltage (Electric Potential Difference)?
In physics, Voltage ($V$) is the work done per unit of charge to move a test charge between two points ($1\text{ Volt} = 1\text{ Joule per Coulomb}$, or $1\text{ V} = 1\text{ J/C}$). Named after Italian physicist Alessandro Volta, who invented the first chemical battery (the voltaic pile in 1800), voltage acts like electrical "pressure" in a pipe system.
According to Ohm's Law, voltage is proportional to current ($I$, measured in Amperes) and electrical resistance ($R$, measured in Ohms):
$V = I \times R$ | $\text{Power } (P) = V \times I = \frac{V^2}{R}$
| Prefix / Unit | Symbol | Scientific Notation | Everyday Electrical Example |
|---|---|---|---|
| Microvolt | µV | $10^{-6}\text{ V}$ ($0.000001\text{ V}$) | Human EEG brain wave signals, radio antenna RF receivers |
| Millivolt | mV | $10^{-3}\text{ V}$ ($0.001\text{ V}$) | Thermocouple temperature sensors, microphone audio outputs, ECG heart signals |
| Volt (Base SI) | V | $10^{0}\text{ V}$ ($1.0\text{ V}$) | AA alkaline batteries ($1.5\text{V}$), USB power ($5.0\text{V}$), automotive car batteries ($12.6\text{V}$) |
| Kilovolt | kV | $10^{3}\text{ V}$ ($1,000\text{ V}$) | Electric train overhead catenary wires ($25\text{ kV}$), automotive spark plugs ($20-30\text{ kV}$) |
| Megavolt | MV | $10^{6}\text{ V}$ ($1,000,000\text{ V}$) | High-Voltage Direct Current (HVDC) cross-country electrical power transmission grids, atmospheric lightning strikes ($100-300\text{ MV}$) |
Tool Guide: Voltage Converter
The Voltage Converter lets electrical engineering students, hobbyists, and licensed electricians scale between metric prefixes instantly:
- Sensors & Analog-to-Digital Converters (ADCs): Microcontroller ADCs (like Arduino or ESP32) read analog signals in millivolts. Convert mV to V to compute accurate sensor voltage divider resistances.
- Electronic Logic Levels: TTL logic operates at $5\text{V}$, standard CMOS at $3.3\text{V}$, and ultra-low-power mobile RAM/SoCs at $1.8\text{V}$ or $1.2\text{V}$. Knowing the exact voltage thresholds prevents burning silicon components.
- International Utility Power: Understanding the difference between US residential split-phase $120\text{V} / 60\text{Hz}$ and European single-phase $230\text{V} / 50\text{Hz}$ prevents blowing appliances when plugging them in overseas.
AC vs. DC: Peak Voltage vs. RMS (Root Mean Square)
Direct Current (DC) delivers a steady, flat voltage (like a $12\text{V}$ car battery or a $3.7\text{V}$ Lithium-ion cell). Alternating Current (AC) oscillates in a sinusoidal wave. When an electrical utility says a wall outlet provides "$120\text{V}$" or "$230\text{V}$", this refers to the RMS (Root Mean Square) effective heating value, not the peak voltage:
$V_{\text{peak}} = V_{\text{RMS}} \times \sqrt{2} \approx V_{\text{RMS}} \times 1.414$
For example, a US $120\text{V}_{\text{RMS}}$ wall receptacle actually reaches peak positive and negative swings of $\approx \pm 170\text{ Volts}$!