Chapter 22 Electromagnetic Waves.doc

Chapter 22 Electromagnetic Waves 22.1 Maxwell’s Rainbow James Clerk Maxwell’s crowning achievement was to show that a beam of light is a traveling wave of electric and magnetic field-an electromagnetic wave-and thus that optics, the study of visible light, is a branch of electromagnetism. In Maxwell’s day, the visible, infrared, and ultraviolet forms of light were the only electromagnetic waves known. Spurred on by Maxwell’s work, however, Heinrich Hertz discovered what we now call radio waves and verified that they move through the laboratory at the same speed as visible light. As figure shows, we now know a wide spectrum of electromagnetic waves, referred to by one imaginative writer as “Maxwell’s rainbow”. In the wavelength scale in figure (and similarly the corresponding frequency scale), each scale marker represents a change in wavelength (and correspondingly in frequency) by a factor of 10. See the arrangement of the wavelength or frequency for different electromagnetic waves in the figure. 22.2 The Traveling Electromagnetic Waves In this section, we will restrict ourselves to discuss the electromagnetic waves to that region of the spectrum (wavelength about 1m) in which the source of the radiation (the emitted waves) is both macroscopic and of manageable dimension. Figure shows, in broad outline, the generation of such waves. To see the production of the electromagnetic waves in figure. The properties of the electromagnetic waves are shown in figure. (1) The electric field, magnetic field and the direction of the travel of the wave are always perpendicular to each other, and the cross product always gives the direction of travel of the wave. Thus the wave is a transverse wave. (2) Both the electric field and the magnetic field always vary sinusoidally. Moreover, the fields vary with the same frequency and in phase (in step) with each other. (3) All electromagnetic waves, including visible light, have the same speed c in vacuum. (4) If we assume that the