Voltage (electric potential difference) drives charge through a circuit.
What is Voltage?
Potential difference between two points; work per unit charge causing current.
Key Formula:
V = W / Q (V volts, W joules, Q coulombs).
Units of Voltage
Volt (V)
SI unit; 1 V = 1 J/C
1 V = 1 J/C
Millivolt (mV)
1/1000 volt; electronics
1 mV = 0.001 V
Kilovolt (kV)
1000 volts; power systems
1 kV = 1000 V
Types of Voltage
Direct (DC)
Constant, fixed polarity.
- Batteries, solar cells
- Polarity constant
- Examples: 1.5V, 12V, 5V USB
Alternating (AC)
Reverses polarity periodically.
- Generators
- 50/60 Hz
- 120/230 V mains
Voltage Conversion Table
| Unit | Volts (V) | Millivolts (mV) | Kilovolts (kV) | Statvolts (statV) |
|---|---|---|---|---|
| 1 V | 1 | 1,000 | 0.001 | 0.003336 |
| 1 mV | 0.001 | 1 | 0.000001 | 0.000003336 |
| 1 kV | 1,000 | 1,000,000 | 1 | 3.336 |
| 1 statV | 299.79 | 299,790 | 0.29979 | 1 |
Did You Know?
The volt honors Alessandro Volta (1800 voltaic pile).
Measuring Voltage
Voltmeters
Measure V in parallel.
Multimeters
Measure V/I/R with ranges.
Oscilloscopes
Waveforms over time.
Voltage in Electrical Circuits
Voltage acts like pressure pushing charge; relates to I and R.
Ohm's Law:
V = I × R (V volts, I amperes, R ohms).
Voltage in Series and Parallel Circuits
Series
- V divides
- I same
- R sums
- Series lights
Parallel
- V same
- I splits
- R total lower
- Home wiring
Applications of Voltage
Electronics
- IC rails 1.2/3.3/5/12 V
- MCUs/CPUs
- Logic
Power systems
- 120/230 V
- 110–1200 kV
- Batteries 1.5–800 V
Medical
- ECG 1–5 mV
- Defibrillators 200–1000 V
- TMS 1–20 kV
Industry
- Electroplating 1–12 V
- Arc welding 10–40 V
- Electrostatic paint 20–100 kV
Safety Warning:
Even 50 V AC/120 V DC can be dangerous. Power off, insulate, follow safety rules.
Voltage in Everyday Life
Household
- AA/AAA 1.5 V
- USB 5 V
- Car 12 V
- Outlets 120/230 V
Electronics
- CPU 0.7–1.5 V
- USB‑C PD 5–20 V
- Laptop 19–20 V
High Voltage
- EV 200–800 V
- Lines 110–1200 kV
- Lightning 100–1000 MV
Practical Tip:
Start multimeter at highest range, step down. Use correct AC/DC mode.