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Ebook Principles & practice of physics (Global edition): Part 2

(BQ) Part 2 book "Principles & practice of physics" has contents: Changing electric fields, electric circuits, wave and particle optics, waves in two and three dimensions, magnetic fields of charged particles in motion, changing magnetic fields, changing electric fields,.and other contents. | www.downloadslide.com 30.1 Magnetic fields accompany changing electric fields 30.2 Fields of moving charged particles 30.3 oscillating dipoles and antennas 30.5 Maxwell’s equations 30.6 electromagnetic waves 30.7 electromagnetic energy Quantitative tools 30.4 Displacement current ConCepts 30 Changing electric Fields www.downloadslide.com 800 Chapter 30 Changing eleCtriC Fields A s we have seen in Section 29.3, electric fields accompany changing magnetic fields. Is the reverse true, too—do magnetic fields accompany changing electric fields? In this chapter we see that magnetic fields do indeed accompany changing electric fields. Consequently, a changing electric field can never occur without a magnetic field, and a changing magnetic field can never occur without an electric field. The interdependence of changing electric and magnetic fields gives rise to an oscillating form of changing fields called electromagnetic waves. Electromagnetic waves are familiar to us as a wide range of phenomena: visible light, radio waves, and x-rays are all electromagnetic waves, the only difference being the frequency of oscillation of the electric and magnetic fields. We see our world by means of these waves, whether by using our eyes to observe our surroundings or by using x-ray diffraction to construct an image of a molecule or a material. Modern communications, from radio and television to mobile telephones, also make extensive use of electromagnetic waves. As we shall see, all these electromagnetic waves consist of changing electric and magnetic fields. 30.1 Magnetic fields accompany changing electric fields ConCepts In order to see that a magnetic field accompanies a changing electric field, let’s revisit Ampère’s law (see Section 28.5), which states that the line integral of the magnetic field along a closed path is proportional to the current encircled S S by the path (Eq. 28.1, A B # d/ = m0Ienc). Figure 30.1 shows a current-carrying wire encircled by a closed