Capacitor Problem: Calculating C1/C2 Ratio | Homework Statement & Equations

[thereddevils]

Homework Statement

A capacitor of capacitance C1 is charged to a potential difference of 10V and then disconnected. A second uncharged capacitor C2 is connected in parallel to the charged capacitor. The new potential difference is 6V. What is the value of the ratio C1/C2?

Homework Equations

The Attempt at a Solution

Some hints to start?

 

[Shivpal]

Since the capacitors are connected in parallel connection, the plates connected with each other will have the same potential, and assuming ideal conditions(i.e no heat loss during charge transfer) the initial energy of the system(consisting C1) will be equal to the final energy of the system (consisting C1 & C2).

 

[Dadface]

Homework Statement

A capacitor of capacitance C1 is charged to a potential difference of 10V and then disconnected. A second uncharged capacitor C2 is connected in parallel to the charged capacitor. The new potential difference is 6V. What is the value of the ratio C1/C2?

Homework Equations

The Attempt at a Solution

Some hints to start?

What do you know so far?

 

[Dadface]

Since the capacitors are connected in parallel connection, the plates connected with each other will have the same potential, and assuming ideal conditions(i.e no heat loss during charge transfer) the initial energy of the system(consisting C1) will be equal to the final energy of the system (consisting C1 & C2).

Even with ideal connecting wires energy will be lost from the system.

 

[thereddevils]

What do you know so far?

When the charged capacitor is connected to the uncharged capacitor, the charged one will discharge until its potential drops from 10V to 6V and the uncharged one is being charged till its pd is 6V. I am not sure about setting up the equations.

 

[Dadface]

When the capacitors are connected charge flows from one to the other as you described but the total charge Q remains constant.You can write Q=CV for the first capacitor and for the parallel combination and take it from there.

 

[thereddevils]

When the capacitors are connected charge flows from one to the other as you described but the total charge Q remains constant.You can write Q=CV for the first capacitor and for the parallel combination and take it from there.

Ok, let me try.

Initially, charged capacitor has Q=10C1 coulomb of charges before being connected.

After connected, the total charge flowing in the circuit is 6C1+6C2.

Since the total charge is a constant, 10C1=6C1+6C2

Therefore, C1/C2=3/2

Am i correct?

Another side question, the charge in each capacitors connected in series is the same? As for parallel, they aren't the same?

 

[Dadface]

Your sums look good.
In series the charges are the same but the pds(voltages) are different.In parallel the pds are the same but the charges are different.

 

[thereddevils]

Your sums look good.
In series the charges are the same but the pds(voltages) are different.In parallel the pds are the same but the charges are different.

Thanks Dadface for all your help.