CK-12 Physical Science - For Middle School

21.1. Electromagnetic Waves http://www.ck12.org

21.1 Electromagnetic Waves

Lesson Objectives

• Describe electromagnetic waves.


• Explain how electromagnetic waves begin.


• State how electromagnetic waves travel.


• Summarize the wave-particle theory of light.


• Identify sources of electromagnetic waves.

Lesson Vocabulary

• electromagnetic radiation


• electromagnetic wave


• photon

Introduction

Both infrared light and visible light are examples of electromagnetic radiation.Electromagnetic radiationis the
transfer of energy by waves traveling through matter or across empty space. The waves that transfer this energy are
called electromagnetic waves. In this lesson, you’ll learn how electromagnetic waves differ from mechanical waves
such as ocean waves and sound waves. For an excellent video introduction to electromagnetic waves, go to this
URL: http://www.youtube.com/watch?v=cfXzwh3KadE (5:20).

MEDIA

Click image to the left for use the URL below.

URL: http://www.ck12.org/flx/render/embeddedobject/5046

What Are Electromagnetic Waves?

Anelectromagnetic waveis a wave that consists of vibrating electric and magnetic fields. A familiar example will
help you understand the fields that make up an electromagnetic wave. Think about a common bar magnet. It exerts
magnetic force in an area surrounding it, called the magnetic field. You can see the magnetic field of a bar magnet
inFigure21.1. Because of this force field, a magnet can exert force on objects without touching them. They just
have to be in its magnetic field. An electric field is similar to a magnetic field (seeFigure21.1). An electric field is