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umang

An air filled parallel plate capacitor charged to potential V₁ is connected to uncharged parallel plate capacitor having dielectric constant k . The common potential of both is V₂ . Find the value of k ???

umang

Someone pls reply !!!!!

aditya_arora04

AS the capacitor is disconnected from electricity supply, the total charge of the system remains constant.

Q = CV₁ ---------------------- (1)

When we join two capacitors, they become parallelly connected.

So, net capacitance,

C_net = C + KC = (K+1)C

So,

Q = (K+1)CV₂ --------------------- (2)

substitute value of Q/c from one in two and you get the answer

Hope you have got it !!!!!!

umang

How did they become parallelly connected ????

aditya_arora04

Hi,

look,

when you connect two capacitors, both plates of one capcitor is connected to both plates of another capacitor, this is the basic condition for parallel connection.

I hope you have got it umang

Please tell me in case of problems

umang

I think I got it .
Since both hav same potential difference V2 , hence they r in parallel .
Am I right ???

aditya_arora04

I am afraid its the other way round.

Both capcitors are in parallel and hence they have a common potential. In this question it has been given that they have acommon potential. but the same question can be given by saying that initial potential of the capacitor is V1 and after connecting it to another uncharged capacitor is V2. Here, you will have to realize yourself that both the capacitors are in parallel.

I hope you must have understood my point.

Do tell me in case of problems.

umang

Cant it be said that both capacitors are in series . I am not getting the clue that they r in parallel .
Pls explain !!!!!

aditya_arora04

Look,

Two capacitors are in series when only one plate of one capacitor is connected to one plate of another plate.

Here, both plates of one capacitor are connected to both plates of another capacitor, and this is said to be paralle connection.

That's how it goes

umang

I am sorry but nowhere in the question it is written that both plates of one capacitor are connected to both plates of another capacitor

So , how r they in parallel ????

aditya_arora04

If you talk about this question, then it is clearly given that they have a common ptential indicating that they are in parallel.

Look, when two capacitors are connected to each other , they are in parallel

umang

I am sorry aditya that I am troubling u so much , But pls help me !!!

priyesh

hi umang

there are two cases of connection series & parallel

now it is given that they have a common potential

so if they are connected in series then Q/C = Q/kC which is not true

hence they are in parallel

note:common potential arises in series in the case of same capacitance

else it occurs in parallel

aditya_arora04

arey why are you saying so, we all are here to help each other.

Tell me honestly that what part of the concept is troubling you, its my pleasure to help you understand it

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