How Does Connecting Capacitors in Parallel Affect Charge and Potential?

[Jalo]

Homework Statement

;-------| |---------;
| |
| |
'-------| |---------'

Consider a capacitator of capacity C1 charged with a charge Q. Suppose you connect it in parallel to another capacitator, C2, initially uncharged.

Find the final charge and difference of potencial at each condensator.

Homework Equations

The Attempt at a Solution

I know that the initial charge Q will be equal to:

Q = q1+q2 , where q1 and q2 is the final charge of capacitator 1 and 2.
The difference of potential, V, is equal in both the capacitators. Therefore I can say that

q1 = Q - q2 = Q - C2/V = [ QV - C2 ] / V

I don't know where to go from here. I don't think I can get anywhere... If anyone could point me in the right direction I'd really appreciate!

Thanks.

 

[aralbrec]

You're thinking in the right direction.

Initially there is a charge on C1 equal to Qi1. There is no charge on C2.

In the end, the voltage across both capacitors is equal, so:

Vf1 = Vf2; Qf1/C1 = Qf2/C2

I'm using Qi as initial charge and Qf as final charge.

Between the initial state and the final state, charge moves from capacitor C1 to capacitor C2. If you assume a charge dQ moves from C1 to C2, you should be able to say something about Qf1 and Qf2 in terms of Qi1.

 

[ehild]

Homework Statement

;-------| |---------;
| |
| |
'-------| |---------'

Consider a capacitator of capacity C1 charged with a charge Q. Suppose you connect it in parallel to another capacitator, C2, initially uncharged.

Find the final charge and difference of potencial at each condensator.

Homework Equations

The Attempt at a Solution

I know that the initial charge Q will be equal to:

Q = q1+q2 , where q1 and q2 is the final charge of capacitator 1 and 2.
The difference of potential, V, is equal in both the capacitators. Therefore I can say that

q1 = Q - q2 = Q - C2/V = [ QV - C2 ] / V

I don't know where to go from here. I don't think I can get anywhere... If anyone could point me in the right direction I'd really appreciate!

Thanks.

Q=CV. AS the potential difference is the same across the parallel connected capacitors, q₁=C₁V and q₂ = C₂V. q₁+q₂=Q. Can you find V in terms of Q and C1, C2? ehild

 

[Jalo]

Q=CV. AS the potential difference is the same across the parallel connected capacitors, q₁=C₁V and q₂ = C₂V. q₁+q₂=Q. Can you find V in terms of Q and C1, C2?


ehild

Oh, so simple... I got to the correct result. Thank you very much!