Lec05-22009 - cture 5-1 Electric flux # of field lines N =...

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Unformatted text preview: cture 5-1 Electric flux # of field lines N = density of field lines x “area” where “area” = A 2 x cos θ To state Gauss’s Law in a quantitative form, we first need to define Electric Flux. θ cture 5-2 Why are we interested in electric flux? E Φ Flux is closely related to the charge(s) which cause it. Consider Point charge Q If we now turn to our previous discussion and use the analogy to the number of field lines, then the flux should be the same even when the surface is deformed. Thus should only depend on Q enclosed. cture 5-3 Gauss’s Law: Quantitative Statement The net electric flux through any closed surface equals the net charge enclosed by that surface divided by ε . How do we use this equation?? The above equation is TRUE always but it doesn’t look easy to use. BUT - It is very useful in finding E when the physical situation exhibits a lot of SYMMETRY . $ enclosed E Q E ndA ε = Φ = ∫ r g Ñ cture 5-4 READING QUIZ 1 Consider a spherical conducting shell with an outer radius b and inner radius a. The shell is insulated from its surroundings and has a net charge of +Q. A point charge –q is inserted into the shell without touching the shell and placed at r = a/2. Which statement is correct ? A| The net charge on the outer surface does not change. B| A charge –q is induced on the inner surface of the shell. C| When the point charge is moved from r = a/2 to r = 0 the charge distribution on the outer surface does not change. D| The net charge on the outside of the shell is Q+q cture 5-5 Infinitely long uniformly charged line ( ) ( ) ( ) 2 E end caps side side E rh π Φ = Φ + Φ = Φ = × r h Gauss’s Law: E h λ ε Φ = 2 2 k E r r λ λ π ε = = Same result but much less work!...
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This note was uploaded on 12/07/2011 for the course PHYS 241 taught by Professor Wei during the Fall '08 term at Purdue University.

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Lec05-22009 - cture 5-1 Electric flux # of field lines N =...

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