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Unformatted text preview: Solution for Homework 4 Adding Electric Fields and Field Maps Solution to Homework Problem 4.1(Identifying Dipole Fields) Problem: Given the field map to the right, the dashed box contains all the charge generating the field. Is the long range field that of a monopole or a dipole? Select One of the Following: (a) Monopole (bAnswer) Dipole (c) Both a monopole and a dipole. Solution Since no lines escape to infinity, the field has the characteristic dipole shape. The region contains no net charge, but contains an electric dipole. Total Points for Problem: 3 Points Solution to Homework Problem 4.2(Force from Three Planes of Charge) 1 Problem: The figure to the right shows two infinite planes of charge. The left plane has charge density σ l = 2 σ . The right plane has uniform surface charge density σ r = σ . A positively charged pith ball is used to test the direction of the electric force at points A , B , and C . Select the direction of the forces that will be observed. Select One of the Following: (a) vector F A to left of page, vector F B to left of page, vector F C to left of page, (b) vector F A to left of page, vector F B to left of page, vector F C to right of page, (c) vector F A to left of page, vector F B to right of page, vector F C to left of page, (d) vector F A to right of page, vector F B to left of page, vector F C to left of page, (eAnswer) vector F A to left of page, vector F B to right of page, vector F C to right of page, (f) vector F A to right of page, vector F B to left of page, vector F C to right of page, (g) vector F A to right of page, vector F B to right of page, vector F C to right of page, A B C +2 σ σ Solution vector F A to left of page, vector F B to right of page, vector F C to right of page. At point A the field for the left plane points to the left and field field of the right plane points to the right. Since the magnitude of the charge density of left plane is greater, the total field points to the left. At point B the field for the left plane points to the right and field field of the right plane points to the right, so the total field points to the right. At point C the field for the left plane points to the right and field field of the right plane points to the left. Since the magnitude of the charge density of left plane is greater, and the electric field of a planar system does not fall off with distance, the total field points to the left. The direction of the force on a positively charged pith ball is the same as the direction of the electric field. Total Points for Problem: 3 Points Solution to Homework Problem 4.3(Gauss’ Law (Version 0) Applied to Point Charges) Problem: A charged system is constructed of three charges 3 Q , 2 Q , and +1 Q . A field map uses 6 lines per Q . How many lines exit the map to infinity or enter the map from infinity? Tell whether lines exit or enter....
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 Spring '10
 Stewat
 Charge, Electric Fields, Work, Electric charge

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