# Jan21 - PHY 131 University Physics II Lecture 2 Electric...

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John Shumway Department of Physics and Astronomy Arizona State University • Tempe • Arizona http://shumway.physics.asu.edu [email protected] PHY 131: University Physics II Lecture 2: Electric charge and Coulomb's law Young and Freedman, Chapter 21.1, 21.2, 21.3 9:00–10:15, Thursday, January 21, 2010 PSF 173 • Department of Physics q 1 q 2 F 12 F 21 | F 12 | = | F 21 | = k | q 1 q 2 | r 2 1

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[email protected] Please read sections 21.1 and 21.2 on your own. Key concepts: • Greeks knew about static electricity by 600 BC, from rubbing amber with wool; the greek word for amber is ήλεκτρον (elektron). • Charge is conserved. Opposite charges attract, like charges repel. • Atoms and molecules are made of negative electrons attracted to nuclei, which contain protons. (F=ma predict that the electrons should collapse into the nuclei! You need quantum mechanics—such as Heisenberg’s uncertainty principle—to explain why electrons in atoms and molecules extend about 10 -10 m around the nuclei.) Electric forces underlie all chemistry and materials science! • Charge is quantized into discrete units e, the magnitude of charge of an electron or proton. • Materials can be classified as conductors or insulators, depending on whether they conduct electricity. (Semiconductors are special materials that can be made to act like either conductors or insulators.) • Sec. 21.2 describes some phenomena involving static electricity in detail. The discussion of induced charges is helpful for HW problem 1-1.
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