# 4.1 – Introduction

Kirchhoff’s circuit laws, first published by Gustav Kirchhoff in 1845, address the conservation of energy and charge in electrical circuits.

Although derived from James Clerk Maxwell’s equations, Kirchhoff’s Laws – Kirchhoff’s Current Law (KCL) and Kirchhoff’s Voltage Law (KVL) – were established using Georg Ohm’s work as a foundation.

These laws are fundamental for analyzing closed circuits, allowing us to determine circuit parameters even in complex configurations, as illustrated below.

Kirchhoff’s laws are applicable under specific conditions, notably, the voltage law is a simplification of Faraday’s law of induction. While suitable for circuits with resistors and capacitors, it’s an approximation in circuits involving changing currents and magnetic fields.

An electromechanical relay, controlled by an electromagnet, functions as a mechanical switch. It allows a small electrical signal to control larger voltage or current. Relays, akin to discrete amplifiers, have diverse applications.Defibrillation, crucial for resuscitation, significantly increases survival chances in fibrillating victims. Immediate defibrillation is imperative, with survival rates decreasing by 10% every minute.

##### Learning Outcomes
1. Apply Ohm’s Law and Kirchhoff’s Law to electronic troubleshooting
2. Describe the principles of a defibrillator
3. Understand the principles of operation of common electromechanical devices – Relays
4. Apply repair and troubleshooting processes to electromechanical devices – Relays