Consider 2 IDENTICAL capacitors . One is fully charged and other is fully UNcharged . If both of them are directly connected by a wire of zero resistance , will any charge flow from the charged capacitor to the other ? [ this concept was used in a JEE problem which gives its answer as 'no' ]
Conceptual Query based on the same concept :
Consider 2 NON-IDENTICAL capacitors .One is fully charged and other is fully UNcharged . If both of them are directly connected by a wire of zero resistance , will any charge flow from the charged capacitor to the other ?
39The answer can't be no(meaning charge will flow..I don't know what your full question is)...when connected by a wire, the identical capacitors become connected in parallel and redistribution of charges takes place to accommodate V1 = V2(equality of potentials relation in parallel circuit). Thus half the charge flows from fully charged capacitor to uncharged capacitor, so that both have equal charges.
1yes..pritish is absolutely right.
and @jsgenius, what do u mean by connecting the two with "a" wire? Do you mean that one plate of capacitor1 is connected to one plate of capacitor 2? even in that case charge will flow. i'm getting in that case the charge flown to be:
2QC2C1+C2
where Q is the charge on the charged capacitor initially, C1 is the charged capacitor and C2 is the uncharged one.
13charg will flow only if circuit is completed.....tht says it ol in 1 lyn...
1Ok..sorry for the confusion...I will post the whole JEE 2001 question here :
Consider the situation shown in the figure.
The capacitor A has charge q on it whereas B is uncharged .The charge appearing on the capacitor B a long time after the switch S is closed is :
i.zero
ii.q2
iii.q
iv.2q
Answer Given : i
Reason Given : When S is closed , there will be no shifting of charges from plate A to B as charge -q is held by +q.
1Now my question is the same...Why the charge flowing to other capacitor is zero here only [ if it is..]...? and CAN ANYONE PLEASE GIVE ME A GNERALISED RULE AS TO WHEN CHARGE WILL FLOWAND WHEN IT WONT ?
39Arey..this means you've connected only one plate each from both capacitors...we were considering complete connection of capacitors, where common potential occurs!
If -q tries to flow from here, as +q is not connected to any circuit element, it cannot lose its charge and to conserve charge -q must remain where it is..in short what deepanshu said.
1so pritish...here is another similar [ but confusing one for me ] ques :
Calculate the amount of charge flow when a conducting sphere of radius R and carrying charge Q , is joined to an uncharged conducting sphere of radius 2R :
I.Q4
II.Q3
III.Q2
IV.2Q3
Ans : IV
[ SO WHAT IS THE DIFFERENCE HERE [ NO DIAGRAM IS GIVEN FOR THIS QUES..] ????[12]
39The difference? That was a plate and this is a sphere...there is no disconnected part if you connect one part of the sphere's surface!
C = 4pi epsilon R I think for spheres? so it depends on radius..
1pritish , pls can u pls explain what u said in the last....I MEAN : IN A SPHERICAL CAPACITOR ALSO THERE IS NO CONTACT BETWEEN NEGATIVE AND POSITIVE SPHERES AND SO IF U CONNECT THE OUTER SPHERE , EVEN THE ELECTRONS WONT BE ABLE TO FLOW DUE TO ATTRACTION rt ?
1in the first case (parallel plate capacitor)
the -ve charge is being held by +ve charge of other plate
both plates should hold same magnitude of charge,I've never seen
any case with 1 plate holding 1C and the other plate holding 2C of
charge.
so if some -ve charge were to flow to capacitor B,then some +ve charge
should flow out(which cannot happen )
since +ve charge in other plate cannot disappear no charge will flow
in second case (sphere)
u can imagine this to be a single sphere with some charge Q,
and at a distance another single uncharged sphere ,connected with a
wire (if Q is positive , then there is no -ve charge near first sphere to hold it
back, ) when they say sphere of radius R charge Q ,they don't mean
2 parallel spheres with charge +Q and -Q.(thats the difference).
1yes , nish, but HOW WILL THE CHARGES GET DISTRIBUTED..?
1now , if i have the same doubt in both ques how will it get cleared , yaar ?