ElectricFluxandGausssLawinEM

# - ELECTRIC FLUX Consider a uniform E-field perpendicular to a surface area A Recall Electric Field E number of electric field lines per unit area

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1 ELECTRIC FLUX Consider a uniform E -field perpendicular to a surface area A. Recall : Electric Field E number of electric field lines per unit area. EA number of E-field lines crossing the surface EA  Electric Flux   2 N m C Electric Flux is proportional to the number of Electric Field Lines penetrating a surface. If the E-field is not perpendicular to the surface area, then the flux will be less than EA because less electric field lines will penetrate A. Consider the wedge shape surface below. The electric field lines are perpendicular to the surface area A but not to A. Since the same number of electric field lines cross both surfaces, the flux must be the same through both surfaces. The surface areas are related by: A = A cos θ Φ = EA =EA cos θ cos E A   Electric Flux

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2 A = surface area vector to the surface area A For a closed surface we define A to point in the outward direction. For an open surface you have two possible choices for the direction of A and thus you must specify its direction. In general a surface may be curved and E will vary in magnitude and direction over the surface. 0 1 lim i i i i i i i ii A i EA                 Electric Flux E dA  
3 Recall that electric flux is proportional to the number of electric field lines crossing a surface. For a closed surface, electric field lines will be either entering or leaving the surface and thus the corresponding flux may be positive or negative.

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## This note was uploaded on 09/02/2011 for the course PHYS 4B taught by Professor Luna during the Spring '11 term at DeAnza College.

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- ELECTRIC FLUX Consider a uniform E-field perpendicular to a surface area A Recall Electric Field E number of electric field lines per unit area

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