Lecture 08 - Electric flux. Gauss s law

Lecture 08 - Electric flux. Gauss s law - Flux in General...

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1 Lecture 8 Electric Flux Gauss’s Law Flux in General Flux: How much of something is passing through a surface. How many hairs are passing through your scalp. If you dip a tennis racquet in a river, how much water flows through it? θ DEMO: Loop Max. flux Flux = 0 Less flux Flux depends on: The flow of the water The area of the tennis racquet A . The orientation ( ) Effective area AA cos 0 p1 Area vector A Is a vector with: Magnitude: Area of surface Direction: Perpendicular to surface Electric Flux Φ Instead of water, we have electric field lines. How many lines go through a given surface? For uniform E and fl t s f s l effective EA Φ = Line density is proportional to the magnitude of the electric field: cos = = G G Φ =⋅ G G Eda In general (for any field and surface): flat surfaces only 2 [] Nm/ C Vm Φ= =
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2 Sign matters! If you reverse the direction of A, you reverse the sign of the flux • For an open surface, choose any direction as long as the choice is made clear •For±a± closed surface , the convention is to take the area vector pointing outwards Flux > 0 lines going out Flux < 0 lines coming in Flux = 0 no lines or a balance between incoming and outgoing lines.
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This note was uploaded on 09/21/2011 for the course PHYS 222 taught by Professor Johnson during the Spring '07 term at Iowa State.

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Lecture 08 - Electric flux. Gauss s law - Flux in General...

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