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Quiz Thursday • Ch.21-22 • one 3x5 inch card notes f/b (do not bring larger) • constants provided – units are not provided 1 Paul A. Tipler • Gene Mosca Physics for Scientists and Engineers Fifth Edition Chapter 21: The Electric Field I: Discrete Charge Distributions Copyright © 2004 by W. H. Freeman & Company 2 Electric Charge qproton = +e qneutron = 0 qelectron = -e 3 Types of Materials Materials covered • Conductors • Insulators 4 Charging by Induction 5 6 Electric Field • • • • E = F/qo. (N/C = V/m) lines leave (+) and enter (-) F = qE. E = E1 + E2 + … (sum of all E fields) 7 Unit Vectors and E Ex. Calculate unit vector pointing from (1, 0) to (6, 2): r1/r1 = {(6, 2) – (1, 0)}/(29). = (5,2)/ (29) 8 Paul A. Tipler • Gene Mosca Physics for Scientists and Engineers Fifth Edition Chapter 22: The Electric Field II: Continuous Charge Distributions Copyright © 2004 by W. H. Freeman & Company 9 E due to Charge Distributions • E = integral of all charge-contributions 10 Uniformly Charged Line of Charge: Eqn. 22-8 11 Uniformly Charged Disk 12 Electric Flux • Flux = integral E “dot” A • Related to charge distribution Case where E is spatially uniform: • f = E·A = EAcosq. • f = +EA (E,A in same direction) • f = -EA (E, A in opposite direction) 13 Flux & Lines of E • equal lines equal flux • Ex. 4 lines EA1cos0° = EA2cosq. 14 Permittivity o 8.85 10 C / Nm 12 2 2 fnet 4kQinside Qinside k 1 4o o 15 Ex. Gauss’s Law E 1 2o R fnet fleft fcyl fright 16 Uniformly Charged Sphere Uniformly Charged Shell 17 Discontinuity of E E n 1 o 4k 18 E near conductor • E = /o. • perpendicular to surface 19