# Jan26 - PHY 131 University Physics II Lecture 3 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 3: Electric fields and electric forces Young and Freedman, Chapter 21.4 9:00–10:15, Tuesday, January 26, 2010 PSF 173 • Department of Physics 1

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[email protected] Notice that the force felt by a charged particle is proportional to the charge of the particle. q 1 F 12 F 13 F 14 q 2 q 3 q 4 F 1 = 1 4 π± 0 ± - q 1 q 2 a 2 - q 1 q 4 2 2 a 2 ² ˆ x + 1 4 π± 0 ± q 1 q 3 a 2 + q 1 q 4 2 2 a 2 ² ˆ y F 1 = q 1 ± 1 4 π± 0 ² - q 2 a 2 - q 4 2 2 a 2 ³ ˆ x + 1 4 π± 0 ² q 3 a 2 + q 4 2 2 a 2 ³ ˆ y ´ Mathematically, we can introduce the concept an electric ±eld E at the point where charge 1 sits: E ( r 1 )= ± 1 4 π± 0 ² - q 2 a 2 - q 4 2 2 a 2 ³ ˆ x + 1 4 π± 0 ² q 3 a 2 + q 4 2 2 a 2 ³ ˆ y ´ F 1 = q 1 E ( r 1 ) 2
[email protected] In chapter 21, the notion of an electric Feld is superFcial; later, we will learn the Feld stores energy and even has its own dynamics. Chapter 21 (Coulomb’s Law): Chapter 23 (Gauss’s Law, charges act on electric Felds): F 1 = q 1 E ( r 1 ) E ( r 1 )= 1 4 π± 0 q 2 r 2 12 ˆ r 12 E · d A = Q encl ± 0 Chapter 24 (Capacitors store energy in electric Felds): u ( r )= 1 2 ± 0 ± ± E ( r ) ± ± 2 Chapter 28 (Maxwell’s equations: “±=ma” for electromagnetic Felds): E · d A = Q encl ± 0 B · d A =0 E · d l = - d Φ B dt B · d l = μ 0 ² i C + ± 0 d Φ E dt ³ 3

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## This note was uploaded on 03/10/2010 for the course MATHEMATIC 242 taught by Professor Heckman during the Spring '10 term at Arizona.

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Jan26 - PHY 131 University Physics II Lecture 3 Electric...

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