Lecture_09_2097

Lecture_09_2097 - Physics 0175 Lecture 9 (July 6, 2009)...

Info iconThis preview shows pages 1–11. Sign up to view the full content.

View Full Document Right Arrow Icon
Physics 0175 Lecture 9 (July 6, 2009) Dielectrics and Capacitors Generalization of Gauss’s Law Electric Current Current Density Resistance and Resistivity Ohm’s Law 1
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Where to Go for Help 1. Your Recitation Section. 2. Office Hours: Lecturer: Prof. Brian R. D’Urso E-Mail: dursobr@pitt.edu Office Hours: Monday and Wednesday, 3:00 – 4:00 pm 315 Allen Hall TAs: Shonali Dhingra, shd28@pitt.edu Office Hours: Tuesday and Thursday, 8:30 pm – 9:30 pm and Friday, 2:00 pm – 4:00 pm 514 Allen Hall (desk #16) Naufer Nusran, nmn6@pitt.edu Office Hours: Tuesday and Thursday, 3:00 pm – 5:00 pm 514 Allen Hall (desk #7) Sui Chi Woo, suw11@pitt.edu Office Hours: Tuesday and Thursday, 1:00 pm – 3:00 pm 419 Allen Hall 3. Appointment with Lecturer or any TA. 2
Background image of page 2
Homework Assignment #3 Reading: Chapters: 25, 26 Problems: See WileyPLUS Homework due Thursday night / Friday morning! 3
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Exam 1 Tuesday, July 7 343 Alumni Hall Topics (Chapters 21-24) Coulomb’s Law Electric Field Gauss’ Law Electric Potential 4
Background image of page 4
Dielectric Constant and Permittivity Take account of the effects of polarization in a linear dielectric by introducing the dimensionless dielectric constant K: E E 0 = κ For a capacitor carrying charge q: •E 0 = Electric field in the absence of dielectric • E = Electric field with the dielectric present It is also useful to introduce the dielectric permittivity ε : ε 0 = Hence, ε 0 is the permittivity of free space (vacuum). To take the dielectric into account (for example, in the capacitance), replace ε 0 with ε . 1 5
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Halliday, Resnick and Walker: Problem 25-44 In the figure below, how much charge is stored on the parallel-plate capacitors by the 12.0 V battery? One is filled with air, and the other is filled with a dielectric for which κ = 3.00; both capacitors have a plate area of 5.00 × 10 -3 m 2 and a plate separation of 2.00 mm. 6
Background image of page 6
Polarization of a Dielectric q’ = polarization surface charge (bound charge) Polarization originates in electric dipole moments at the molecular level: • permanent dipoles partially oriented by the electric field opposed by random thermal motion • induced electric dipoles 7
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Gauss’s Law Reformulated for Dielectrics When treating dielectrics, it is convenient to write Gauss’s Law in a form that does not explicitly include the polarization charge q’. Apply Gauss’s Law to the “Gaussian pillbox” to obtain: = = = A q E q A E d 0 0 0 0 0 ε A E r r κ q q q = 0 E E = = q d 0 A E r r No dielectric: With dielectric: = = = A q q E q q EA d 0 0 0 A E r r Use to obtain 8
Background image of page 8
Parallel Plate Capacitor: Effect of a Dielectric κ q q q = Note that the result below, copied from the preceding slide, can be solved for the polarization charge. = 1 1 q q 9
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Consider an isolated capacitor, capacitance C 0 , carrying charge q. The stored energy is .
Background image of page 10
Image of page 11
This is the end of the preview. Sign up to access the rest of the document.