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Electricity

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 Joined: 29 Aug 2007 Post: 1
29 Aug 2007 10:50:18 IST
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What is negative flux?
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What is negative flux?

Blazing goIITian

Joined: 9 Nov 2006
Posts: 814
29 Aug 2007 11:50:37 IST
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Flux entering a surface is taken as positive and flux leaving the surface is taken negetive.

This helps in solving problems where the fluxes entering and leaving a surface is known and we have to calculate charge within the conductor.

Suppose a Gaussian surface encloses an unknown charge. Flux entering and leaving the surface are #1 and #2. We want to know the magnitude of charge enclosed by the Gaussian surface.

From Gauss Law

Net Flux = q/epsilon

Here Net flux = #1 - #2

So charge = (#1 - #2)*epsilon.

Hope u are clear.........

Blazing goIITian

Joined: 13 Jul 2007
Posts: 547
29 Aug 2007 11:51:26 IST
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when electric field is entering a surface, the flux associated with the surface is negative and when field is leaving the surface, flux is positive.
u can visualize field by field lines entering or leaving a surface

Blazing goIITian

Joined: 1 Apr 2007
Posts: 4025
31 May 2011 23:33:29 IST
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It only means that the direction of give flux is opposite to some reference which we consider as positive.property of an electric field that may be thought of as the number of electric lines of force (or electric field lines) that intersect a given area. Electric field lines are considered to originate on positive electric charges and to terminate on negative charges. Field lines directed into a closed surface are considered negative; those directed out of a closed surface are positive. If there is no net charge within a closed surface, every field line directed into the surface continues through the interior and is directed outward elsewhere on the surface. The negative flux just equals in magnitude but of opposite direction.

Scorching goIITian

Joined: 1 Jun 2011
Posts: 207
2 Jun 2011 22:36:49 IST
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AGREE WID VIKRAM SIR

New kid on the Block

Joined: 10 Jun 2011
Posts: 12
10 Jun 2011 09:39:24 IST
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flux is E.dA means EdAcostheta when a electric field line enter a particular gaussian surface it make a angle with area vector whch is greater then 90 so cos theta is negative so flux negative and when it leave it make angle with area vector which is less than 90 so flux is positive(area vector is always point outward normal to the surface)

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