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Unformatted text preview: Solution for Homework 4 Adding Electric Fields and Field Maps Solution to Homework Problem 4.1(Simple Application of Field Lines) Problem: A region of space contains two charged objects with charge + Q and- Q . If four field lines are assigned to each Q , how many net field lines exit the region? Select One of the Following: (a-Answer) Zero. (b) Two. (c) Four. (d) One (e) More information is needed. Solution Zero! There are four field lines coming out of the positively charged object and four going in to the negatively charged object. Since they have equal and opposite charge, there are no net field lines. If you go out far enough, all of the field lines coming out of the positive charge connect to the field lines entering the negative charge. Total Points for Problem: 2 Points Solution to Homework Problem 4.2(Force on Charged Object in Electric Field) Problem: A negative point charge is placed in an electric field with field lines pointed in the + x direction. The electric force on the charged particle is in which direction? Select One of the Following: (a) There is no force on the charged particle. (b) The force on the charged particle is in the + x direction. (c-Answer) The force on the charged particle is in the- x direction. (d) It is impossible to tell the direction of the force on the charged particle based on the information provided. Solution c. The force on a charged particle due to an electric field is equal to q vector E . The particle is negatively charged, so the charge on it due to the electric field is-| q | vector E . This is opposite the direction of the electric field lines. Since the electric field lines are pointed in the + x direction, the electric force felt by the negatively charged particle is in the- x direction. Total Points for Problem: 3 Points Solution to Homework Problem 4.3(Electric Dipole in an Electric Field) Problem: 1 (a)What is the direction of the net electric force on an electric dipole with dipole moment in the + y direction if placed in a uniform electric field in the + x direction? Select One of the Following: (a) + x (b)- x (c) + y (d-Answer) y (e-Answer) The electric force is zero. (b)Does the electric dipole feel the same net electric force in a nonuniform electric field? Select One of the Following: (a) Yes. (b-Answer) No. Solution to Part (a) (a) Description of an Electric Dipole: A dipole can be modeled as a small rod with one positive end and one negative end. The ends are oppositely charged and have charges of equal magnitude. (b) Force on a Dipole in a Uniform Electric Field: At any point in a uniform electric field, both ends of the dipole will feel forces of the same magnitude but in opposite directions, so the entire dipole will feel zero net force....
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