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Unformatted text preview: Solution for Homework 7 Conductors and Dielectrics Solution to Homework Problem 7.1(Difference Between Dielectric and Conductors) Problem: Explain how the induced charge on a conductor and the bound charge on a dielectric differ atomically. Select One of the Following: (a) The charge can move freely in a dielectric, but has limited movement in a conductor. (b-Answer) A charge can move freely in a conductor but has movement is limited in a dielectric. (c) An induced charge on a conductor is larger than the same induced charge in a dielectric. (d) The induced charge on a dielectric is stronger than the same induced charge on a conductor. (e) Both can have an induced charge move over them but in a conductor it is limited to the surface of the conductor. Solution Charge can move the entire length of a conductor, while movement in a dielectric is limited to atomic or molecular distances. Total Points for Problem: 3 Points Solution to Homework Problem 7.2(Compute Bound Charge of Plexiglass) Problem: A piece of plexiglass ( = 3 . 2) is placed above an infinite plane of charge with charge density =- . 1 C m 2 . Compute the bound charge density on the bottom surface of the dielectric. Be careful of the sign. Select One of the Following: (a)- 1 . 7 10- 8 C / m 2 (b) 1 . 7 10- 8 C / m 2 (c)- 3 . 4 10- 8 C / m 2 (d-Answer) 3 . 4 10- 8 C / m 2 (e)- 5 . 5 10- 6 C / m 2------- b t = 3.2 1 Solution (a) Calculate the Fields: Outside the slab, the field is that of an infinite plane. So immediately below the slab the field is vector E =- 2 z The field inside the slab is reduced by a factor of , vector E =- 2 z---------- + + + + z t b = 3.2 (b) Apply Gauss Law: Use a Gaussian Pillbox, a cylinder with end area A as drawn above. The charge enclosed in the cylinder is Q enc = b A . Applying Gauss Law to the pillbox yields E t A- E b A = E A- E A = Q enc = b A (c) Substitute the Fields: Cancelling...
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