Electromagnetic Theory Overview

Overview

This lecture covers the historical development, basic principles, and practical applications of electromagnetic (EM) theory, highlighting key scientific contributors and foundational concepts.

Development of Electromagnetic Theory

• Many scientists contributed to EM theory, but the focus is on five key figures.
• Hans Christian Ørsted (1820) discovered that electric currents create magnetic fields.
• André-Marie Ampère showed that electric currents can generate magnetic attraction and repulsion, coining "electrodynamics."
• Michael Faraday found that a changing magnetic field induces an electric current, known as electromagnetic induction.
• James Clerk Maxwell unified electricity and magnetism into a mathematical EM theory and predicted EM waves travel at the speed of light.
• Heinrich Hertz experimentally confirmed the existence of EM waves (radio waves), verifying Maxwell's theory.

Basic Principles of Electromagnetic Theory

• Many natural phenomena, including EM waves, exhibit wave-like behavior.
• Light and other EM waves do not need a medium and consist of oscillating electric and magnetic fields.
• EM waves travel through a vacuum at approximately 3 × 10⁸ meters per second.
• EM waves are transverse; electric and magnetic fields oscillate perpendicular to each other and the direction of wave travel.
• Accelerating (oscillating) charges produce EM waves due to changes in their electric fields.

Applications of Electromagnetic Theory

• EM theory underpins technologies in households, industry, transportation, communication, medicine, and space.
• Electromagnetism has countless practical uses in daily life and advanced research.

Key Terms & Definitions

• Electromagnetic waves (EM waves) — Waves composed of oscillating electric and magnetic fields that propagate through space.
• Electromagnetic induction — The process where a changing magnetic field creates an electric current.
• Transverse wave — A wave where oscillations are perpendicular to the direction of propagation.
• Electrodynamics/Electromagnetism — The study of electric currents and their magnetic effects.

Action Items / Next Steps

• Reflect: Answer in your science notebook—How did EM theory advance modern technology?
• Fill out a graphic organizer on the contributions of Ørsted, Ampère, Faraday, Maxwell, and Hertz.
• Review pre-test answers.
• Prepare for the next lesson on wavelengths and frequencies of EM waves.