What are the conversion relationships between voltage units?
The SI unit of voltage is the volt (V), with prefix units using a conversion factor of 1000: 1 kV = 1000 V (volts) = 1,000,000 mV (millivolts) = 1,000,000,000 μV (microvolts). Adjacent units differ by a factor of 10³: 1 V = 1000 mV, 1 mV = 1000 μV, 1 kV = 1000 V. That is, kV → V → mV → μV multiply by 1000 to the right, divide by 1000 to the left, standard SI kilo-based system consistent with other electrical units like current, capacitance, resistance.
How is the volt (V) defined?
The volt (symbol V) is the SI unit of voltage/electric potential/electromotive force, named after Italian physicist Alessandro Volta (inventor of the voltaic pile). 1 volt = 1 joule/coulomb (1 V = 1 J/C), the potential difference required to do 1 joule of work when moving 1 coulomb of charge through a circuit. After the 2019 SI redefinition, the volt is derived from the Josephson constant Kⱼ (exactly 483597.8525×10⁹ Hz/V), which can be accurately reproduced via superconducting Josephson junctions with extremely high precision.
How do you calculate voltage in Ohm's law? What's the relationship with current and resistance?
Ohm's law is the most basic circuit formula: U = I × R (voltage = current × resistance), power P = U × I = U²/R = I²R. Where voltage U is in V, current I in A, resistance R in Ω, power P in W. For example, when 10mA current flows through a 1kΩ resistor, the voltage across the resistor U = 0.01A × 1000Ω = 10 V; a 100W bulb connected to 220V mains draws about 0.45A. This tool helps you quickly switch calculated voltage values between kV/V/mV/μV.
What magnitudes are common in typical scenarios?
Common voltage magnitude reference: ECG signals about 0.5-2mV (500-2000μV); thermocouple outputs tens of μV to tens of mV; EEG about 10-100μV; dry cell 1.5V, USB 5V, mobile phone lithium battery 3.7V (4.2V full), lead-acid battery 12V (rated)/13.8V (float); laptop adapter 19V; mains 110V/220V; three-phase industrial power 380V; electric vehicle battery packs 48V/60V/72V/400V/800V; power distribution 10kV, transmission 110kV/220kV/500kV/1000kV (ultra-high voltage); static electricity can reach tens of thousands of volts; lightning 100 million to 1 billion volts.
How much voltage is dangerous to the human body? What is safety voltage?
IEC 60038 and China GB3805 specify: Safety Extra Low Voltage (SELV) rated value does not exceed 42V (usually 36V, 24V, 12V), in dry environments generally considered safe below 36V, work in wet/metal containers should use 12V. What's truly fatal is not voltage itself but current, but voltage determines the magnitude of current flowing through the human body — 220V mains in dry environments can cause 2-22mA current (severely fatal), above 1000V there is arc hazard, safety distance is the main protection method. AC power frequency (50/60Hz) is more dangerous than DC and high frequency at the same voltage.
Why use μV/mV level units for weak signals?
Sensors and bioelectrical signals are often very weak: Type K thermocouple about 41μV per 1℃, full scale 1000℃ only 41mV; ECG R-wave peak 0.5-2mV, EEG alpha waves 10-100μV; strain gauge bridge outputs often only a few mV; broadcast signals received by radio antennas can be as low as μV/m field strength; photodiode outputs nA~μA level converted via I/V to get mV signals. These weak signals need high-gain low-noise op-amps to amplify to V level for ADC acquisition, circuit design and debugging must be familiar with μV↔mV↔V conversion.
What's the relationship between battery voltage and capacity? What do mAh and V mean?
Battery capacity (mAh) indicates how much charge (electric charge) can be discharged, nominal voltage (V) is the battery's working potential. Energy (Wh) = voltage (V) × capacity (Ah). For example, 3.7V/3000mAh mobile phone battery energy = 3.7V × 3Ah = 11.1Wh; 12V/100Ah lead-acid battery energy = 12 × 100 = 1200Wh = 1.2kWh. Battery voltage differs between full charge and discharge (e.g., lithium 3.0-4.2V, lead-acid 10.5-14.4V), need to combine voltage curve to determine state of charge (SOC), this tool is for voltage unit conversion.
Why do many people write uV instead of μV?
μ is the Greek letter Mu, there's no key for it on standard English keyboards, early SPICE simulation, C programming, ASCII serial ports, component silkscreens etc. were inconvenient to input μ, so the electronic engineering industry universally uses the English letter u instead of μ (similar pronunciation), uV = μV is conventional notation (e.g., 100uV = 100μV). Oscilloscopes, multimeters, signal generators, power panels commonly show four markings uV/mV/V/kV, mV/V/kV ranges are most commonly used.
How to distinguish AC voltage and DC voltage?
Direct current (DC) voltage direction is constant over time (batteries, USB, power adapter outputs), alternating current (AC) voltage polarity changes periodically (household mains). AC voltage usually refers to RMS (root mean square), 220V mains RMS 220V corresponds to peak about 311V, peak-to-peak about 622V. Multimeter AC range measures RMS, when selecting TVS/varistor/capacitor voltage withstand devices calculate by peak not RMS — for example 220V circuits should select electrolytic capacitors with withstand voltage ≥350V (400V common).
What are kV-level high voltage applications? What safety precautions?
kV-level high voltage applications: 10kV is standard urban distribution voltage, 220kV/500kV/1000kV (UHV) are long-distance transmission voltages; CRT monitor anodes have 20-30kV high voltage; X-ray machine tubes tens to 150kV; electrostatic spraying/electrostatic precipitation tens of kV; electron guns, particle accelerators can reach MV level. High-voltage operations must de-energize, tag out, test for voltage, attach grounding wires, maintain safe distance (10kV≥0.7m, 110kV≥1.5m, 220kV≥3m), wear insulating protective equipment, strictly prohibit live working.
What's the relationship between decibels (dB) and voltage?
Voltage gain expressed in dB: G(dB) = 20·log₁₀(Vout/Vin), because power P=U²/R, so it's 20 times log (power dB is 10 times log). 6dB≈2x voltage, 20dB=10x voltage, 40dB=100x voltage, 60dB=1000x voltage (exactly spanning three kilo-based magnitudes). For example, op-amp open-loop gain 100dB≈10⁵ times, meaning 1mV input amplifies to 100V output (practically limited by power supply). RF/audio engineers often need to convert between dB and voltage multiples.
Will my input voltage values be uploaded? Is privacy secure?
Not uploaded at all. The entire conversion logic uses pure front-end JavaScript running in your local browser, there are no network requests sent for input voltage values, servers cannot see any of your circuit parameters, test data or power maintenance information. Input content is cleared immediately after closing the tab, no cookies or localStorage used for storage. Suitable for enterprise R&D, power maintenance, military electronics, teaching exams, high-voltage field operations and other data privacy-sensitive scenarios.
