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Chapter 24 | Electromagnetic Waves 1081
24 ELECTROMAGNETIC WAVES
Figure 24.1 Human eyes detect these orange “sea goldie” fish swimming over a coral reef in the blue waters of the Gulf of Eilat (Red Sea) using visible light. (credit: Daviddarom, Wikimedia Commons)
Connection for AP® Courses
Electromagnetic waves are all around us. The beauty of a coral reef, the warmth of sunshine, sunburn, an X-ray image revealing a broken bone, even microwave popcorn—all involve electromagnetic waves. The list of the various types of electromagnetic waves, ranging from radio transmission waves to nuclear gamma-rays (γ-rays), is interesting in itself. Even more intriguing is that all of these widely varied phenomena are different manifestations of the same thing—electromagnetic waves. (See Figure 24.2.)
What are electromagnetic waves? How are they created, and how do they travel? How can we understand and conceptualize their widely varying properties? What is their relationship to electric and magnetic effects? These and other questions will be explored in this chapter.
Electromagnetic waves support Big Idea 6 that waves can transport energy and momentum. In general, electromagnetic waves behave like any other wave, as they are traveling disturbances (Enduring Understanding 6.A). They consist of oscillating electric and magnetic fields, which can be conceived of as transverse waves (Essential Knowledge 6.A.1). They are periodic and can be described by their amplitude, frequency, wavelength, speed, and energy (Enduring Understanding 6.B).
Simple waves can be modeled mathematically using sine or cosine functions involving the wavelength, amplitude, and frequency of the wave. (Essential Knowledge 6.B.3). However, electromagnetic waves also have some unique properties compared to other waves. They can travel through both matter and a vacuum (Essential Knowledge 6.F.2), unlike mechanical waves, including sound, that require a medium (Essential Knowledge 6.A.2).
Maxwell’s equations define the relationship between electric permittivity, the magnetic permeability of free space (vacuum), and
Chapter Outline
24.1. Maxwell’s Equations: Electromagnetic Waves Predicted and Observed 24.2. Production of Electromagnetic Waves
24.3. The Electromagnetic Spectrum
24.4. Energy in Electromagnetic Waves