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Lect_4_note - Chapter 24 -1 Gausss Law Description of...

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Chapter 24 -1 Gauss’s Law
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Description of Electric Field 2 ˆ e e o q k qr == F Er
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Electric Flux Φ N ± Electric flux is the product of the magnitude of the electric field and the surface area, A , perpendicular to the field ± Φ E = EA
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Electric Flux ± The field lines may make some angle θ with the perpendicular to the surface, Then Φ E = EA cos ± Movie 4_1 Φ N
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A point charge ± A positive point charge, q , is located at the center of a sphere of radius r ± Calculate Φ at this surface
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A point charge 2 ˆ e e o q k qr == F Er Φ E = E A = E 4 π r 2 4 Ee o q π kq ε Φ= = ε ο = 1/(4 π k e )
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A point charge 4 Ee o q π kq ε Φ= = ± Does this conclusion hold if the sphere size changes? ± Does this conclusion hold if the charge is shifted inside the sphere? ± Does this conclusion hold if the sphere is changed to other shapes?
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size of sphere r 2 The flux is the same as before 2 2 0 | | 4 1 | | r E q πε = 2 2 2 2 0 2 | | 4 | | 4 1 r r π ´ = Φ q 0 2 ε q = Φ 0 1 2 q = Φ = Φ
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Now move the charge The number of electric field lines penetrating the surface does not change.
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This note was uploaded on 01/28/2011 for the course PHYS 011 taught by Professor Nianlin during the Fall '08 term at HKUST.

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Lect_4_note - Chapter 24 -1 Gausss Law Description of...

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