no tagsHomework003SteveSekula, 6 September 2010 (created 5 September 2010)Homework 3Expectations for the quality of your handed-in homework are available athttp://www.physics.smu.edu/sekula/phy1308/HomeworkPolicy.pdf. Failureto meet these guidelines will result in loss of points as detailed in thatdocument. This assignment covers material from Wolfson Chapter21.4-21.6 and 22.1. Each problem is worth 20 points, and the totalassignment is worth 60 points.This homework is due by 9am (start of class) on Monday, September13Reading Assignment:Chapter 21.4-21.6, 22.1Problems:Problem SS-8Let us model a copper electrode as a slab of charge that extends infinitelyin two dimensions and has a thickness, , in the third dimension, a shownbelow. The slab carries a uniform volume charge density .Find an expression for the electric field strength inside the slab, as a1.General Physics - E&M (PHY 1308) LectureNotesGeneral Physics - E&M (PHY 1308) LectureNotesd Ú General Physics - E&M (PHY 1308) - Lecture Notes file:///home/sekula/Documents/Notebooks/PHY1308...1 of 3 09/06/2010 05:57 PMfunction of the distance from the center plane of the slab.Find an expression for the electric field strength outside the slab, as afunction of the distance from the center plane of the slab.2.If, instead, we placed the same charge on a real copper plate with thesame dimensions (copper is an electrical conductor), how would theelectric fields inside and outside the plate change?3.Problem SS-9Electrophoretic ink, or E-Ink, is a technology that allows images to beformed on a flat surface simply through the application of weak electricfields (c.f. the Amazon Kindle, or the Barnes and Noble Nook). The electricfields, depending on whether they originate from areas of positive ornegative charge, cause small droplets of white material (the actual "ink"),suspended in a dark oil, to drift closer to or further away the surface of the"paper" (see illustration below).x x General Physics - E&M (PHY 1308) - Lecture Notes file:///home/sekula/Documents/Notebooks/PHY1308...2 of 3 09/06/2010 05:57 PMConsider one of these small droplets, a white one made from titaniumdioxide. Model it as a solid sphere, of radius , that carries a volumecharge density , where is a constant and is the distancefrom the center of the droplet. Find an expression for the electric fieldstrength at the surface of the sphere.1.It takes about 0.2 seconds for the page-turn to happen on an E-Inkbased device. A "page-turn" corresponds to the movement of whiteparticles closer or further away from the paper surface, as appropriate,to achieve the lettering on the new page. If each white droplet carriesa charge of , has a mass of , and has to cross a distanceof when going from the bottom to the top of the pixel, estimatethe strength of the electric field to which the droplet is subjected.Assume there are no collisions during the movement of the droplet, andthat the droplets are small compared to the dimensions of each pixel(which they are, in reality).2.Using your answer from the last question, determine the electricpotential across each pixel. If you didn't obtain an answer to theprevious question, assume that , where is a unit vectorpointing from the bottom of the pixel to the top (this is not the correctnumerical answer to the previous question).3.How much work is done in moving the droplet through the potentialdifference in the previous question? If you were unable to obtain anumerical answer, assume (this is not thenumerical answer to the previous question).4.R Ú e = Ú0r=RÚ 0r À16e 6:7 0 kg  1À1540:0Öm E À3:0i)N=C ~= (^i ^V :2 0 =C = 1  1À4N Á mGeneral Physics - E&M (PHY 1308) - Lecture Notes file:///home/sekula/Documents/Notebooks/PHY1308...3 of 3 09/06/2010 05:57
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