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Electricity

Blazing goIITian

 Joined: 19 Jan 2008 Post: 351
18 May 2008 10:55:41 IST
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gauss theorem
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is gauss theorem  applicable for insulators and semi conductors .

qn. 4 u >>>

a solid sphere has +ve charge uniformly distributed inside it . a spherical portion is cut out off the sphere and a cavity hence created . find the nature of electric field inside the cavity .

Blazing goIITian

Joined: 27 Mar 2008
Posts: 412
18 May 2008 12:05:44 IST
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Yes. gauss's thrm is applicable for insulators n semi-conductors.

The electric field is zero at all points inside the cavity, if the solid sphere is a conductor.

Blazing goIITian

Joined: 30 Mar 2008
Posts: 1418
18 May 2008 12:13:27 IST
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the electric field is inside the cavaty is zero....

Blazing goIITian

Joined: 19 Jan 2008
Posts: 351
18 May 2008 19:41:20 IST
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nop friend the qn says that the solid sphere has +ve charge uniformly distributed INSIDE IT implying its not a conductor .

the answer is that the +ve charges induce negative charges and net field is -ve . but i want a little more explaination and reason so as to why charges are induced and from where these charges come from .

Scorching goIITian

Joined: 22 Dec 2006
Posts: 211
18 May 2008 20:14:18 IST
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See there is nowhere given that the sphere is conductor so it is not necessary that the charges will come on the outer surface(Given in the ques. itself).

Now when a cavity is cut inside the spherical shell some charges reside on its boundary which result in a

UNIFORM electric field throughout the cavity

Blazing goIITian

Joined: 19 Jan 2008
Posts: 351
18 May 2008 21:56:49 IST
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exactly charges reside on the surface of the cavity but what makes them induce negative charge .
u say uniform electric field i say its nature is negative .
this is that 100 percentileqn. i saw the soln. but i don get the fact so as to from where these electrons are coming from ???

Blazing goIITian

Joined: 31 Jan 2008
Posts: 334
19 May 2008 01:17:08 IST
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well the solid sphere is not a conductor ........

and if a conductor charges udnt hve aligned inside it

they ud only exist at surface. so the ans is ritly uniform electric field thru out........

and the derivation of it can be done using superposition principle ....

CHEERS!!!!!!!!

Cool goIITian

Joined: 8 Feb 2008
Posts: 34
19 May 2008 02:44:11 IST
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yes gauss theorm is valid for insulators ans semiconductors.SEE its derivation in any book; we didnt take conductors as our assumption anywhere.

field inside cavity is uniform. this can be prove dby considering cavity=+ve charge +-ve charge.

Consider any pt P in cavity.center of sphere exert attractive force on pt P(field towardsitself) and center of -ve charge(ie center of cavity ) exert repulsive force(field away from itself). By simple vector calculations we can prove electric field is uniform.

if u couldnt follow plz let me know. I would attach figure along with it

Cool goIITian

Joined: 19 May 2008
Posts: 63
19 May 2008 04:20:07 IST
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Well...considering the sphere is a conductor the charge will always distribute itself on the surface and even if there is a cavity created, the field inside the sphere will be ZERO.  And yeah gauss's law can be applied for both semi-conductors and insulators ...thrs no reason why it cannot be.

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