02·Circuit, ground (GND) and polarity

Introduction

For current to flow, the circuit must be closed — from the source positive terminal, through the components, back to the negative terminal. This lesson explains what ground (GND) is as a 0 V reference point, why voltage is always measured between two points, and how polarity determines the operation of polarized components (LED, diode, electrolytic capacitor) and modules connected to Arduino. You will also learn the concept of common ground and the effects of a short circuit.