Electronics basics · Lesson
8 min read
Voltage, current and resistance
The three quantities behind every circuit, explained with water in pipes.
What You Will Learn
- Explain voltage, current and resistance in your own words
- Know the units V, A (mA) and Ω
- Recognise a complete circuit
Electricity is the flow of tiny charged particles (electrons) through a conductor such as copper wire. Three quantities describe what happens in a circuit.
| Quantity | Symbol | Unit | Water analogy |
|---|---|---|---|
| Voltage | V | volt (V) | Water pressure — the push |
| Current | I | ampere (A), milliamp (mA) | How much water flows per second |
| Resistance | R | ohm (Ω) | A narrow pipe that limits the flow |
Current only flows in a closed loop: from the + side of a supply, through components, and back to the − side (GND). Break the loop anywhere and everything stops.
An Arduino Uno works at 5 V. An ESP32 works at 3.3 V. A USB port can supply about 500 mA in total.
Never connect + directly to GND (a short circuit). The current is limited only by the wires and the supply, which can overheat or reset your board.
Check Your Understanding
Test what you learned in this lesson