(1) It increases the break down potential of the surrounding medium so that more potential can be applied and hence more charge can be stored.

Transcription

1 Cpcito Cpcito: Cpcito ( o conense ) is evice fo stoing chge. It essentilly consists of two conucting sufces such s two pltes o two spheicl shell o two cylines etc. kept exctly pllel to ech othe septe y vey smll istnce ( <.mm ). The spce etween the two conuctos cn e fille with ielectic meium. One of the two conuctos is chge n the othe is ethe. The ielectic etween two conuctos seves two puposes () It inceses the ek own potentil of the suouning meium so tht moe potentil cn e pplie n hence moe chge cn e stoe. () It inceses the cpcitnce of the cpcito. Explntion: (ek own potentil) We know tht y pplying highe potentil gete chge cn e stoe in oy. ut thee is limit up to which this is tue, if we incese the potentil eyon the limit the chge will not e stoe on the oy the suouning insulting meium ecomes conucting meium. s esult the ove flowe chge on the oy hs tenency to go into the eth hence in tht cse the excess potentil pplie goes to the eth y spking though the new evelope conucting meium, i.e. the potentil of the suouning insulting meium eks own. Selfstuy.in High School Tutoil Clss Notes Electosttics Pge

2 Cpcito ()Pllel Plte Cpcito: Given : σ sufceensity of chgeon theconuctingpltex eof thepltes theistnceof septionetween the pltes theeltivepemittivi ty (ielecti c constnt) of themeiumetween the pltes Sincegpetween th eh twopltesis vey veys mllthefieletween th eh twopltesi is unifom Let E e theintensityt yof theelecticfielin etween the twopltes. Weknowtht theintensity t point ne n nfinely longchgeconuctingplte σ σ E Let e E E Chge C () thepotentiliffeence etwen thetw wopltes If the spce etween the pltes contins moe thn one ielectic meium then it is known s compoun ielectic. Let t thickness of ielecticc sl (t < ) C t σ () σ σ o C (3)o C σ (4) Selfstuy.in High School Tutoil Clss Notes Electosttics Pge

3 Cpcito () Spheicl Cpcito: Cse I: The inne shell is chge n the out shell is ethe. & ii of the inne n oute shell espectively. i - electic constnt of the meiumm etween the two shells. chge on the sufce of the inne shell Chge + on inuces oun chge - & fee chge + on the inne n oute sufce of the shell espectively. The fee chge + flows to eth. Consie ny point P on Potentil t P ue to the (i) chge + on, (ii) chge - on, P + Potentil of shell, it is ethe. Potentil iffeence The cpcitnce of the spheicl cpcito C () ( ) + 4 π 4 π ( ( ) ) Selfstuy.in High School Tutoil Clss Notes Electosttics Pge 3

4 Cpcito Cse II: The oute shell is chge the inne shell is ethe We know tht chge lwys lies on the oute sufce of close oy ecuse it is nee to the eth (oy t zeo potentil), ut in this cse since shell fces eth on its outsie n oy ( shell ) t zeo potentil on its inne sie hence the chge on will e istiute on its oute sufce s well s inne sufce. Let The chge + Consie ny point P on Potentil t P ue to the (i) - ( ii) + (iii) + & + on, ( ) on, on, chge on the oute n inne sufce of the shell espectively. ' ( 3) on the inne sufce of inictes - ' ' 3 + ' ' ' ecuse is ethe. + ( ) on. Selfstuy.in High School Tutoil Clss Notes Electosttics Pge 4

5 Puttingeqution (3)in eqution() (i) Chge- (ii) Chge+ (iii) Chge+ Totlpotentilof theshell: Potentiliffeenceetween the shells Puttingeqution (4)in eqution (5): ( ) -. on, on, on, (5) Cpcito + + ( ) (4) Potentilt ny point on thesufceof theshell ue to Cpcitnce of thecpcito :C If C C C C i o o o > C & C ( - ) ( - ) i i 3 ( ) ( - ) 3 - e the cpcitnce of spheicl cpcito when oute shell is ethe n inne shell is ethe then Selfstuy.in High School Tutoil Clss Notes Electosttics Pge 5

6 Cpcito Cpcitnce of cylinicl cpcito: n ii of λ chge pe unit length l length of the cyline eltive pemittivity of the meiumm etween the two cylines consie ny point P t istnce fom the xis. Fom the ppliction of Guss's theoem we know tht intensity t P ue to the chge inne cyline λ E π v ut E - v -E Totl potentil iffeence etween the two cylines v v λ v log π π l C log e E e λl C λ log π inne n oute cyline espectively λ π e Selfstuy.in High School Tutoil Clss Notes Electosttics Pge 6