01·Voltage, current, resistance and Ohm's law

Introduction

Three quantities you cannot understand any circuit without: voltage (U, in volts V), current (I, in amperes A) and resistance (R, in ohms Ω). Voltage is the "push" that drives charge, current is the stream of charge actually flowing, and resistance is the obstacle limiting that stream. They are linked by Ohm's law U = I · R. This lesson builds intuition with the hydraulic analogy, drills formula rearrangements on real Arduino values (5 V, 220 Ω / 330 Ω / 1 kΩ resistors, currents in mA) and introduces power P = U · I so you know how much heat a resistor dissipates.