Parallel Capacitors connected to Battery then D/C

In summary: Thanks for trying to help! Sounds good. Now you just need to figure out how that remaining charge will distribute over the caps.
  • #1
RavageU
4
0

Homework Statement


Capacitors of 19.1 uF and 2.1 uF are charged as a parallel combination across a 229 V battery. The capacitors are disconnected from the battery and from each other. They are then connected positive plate to negative plate and negative plate to positive plate.
Find the resulting charge on the first capacitor.

Homework Equations


Q = CV

The Attempt at a Solution


Since they are connected in parallel, I found the charge for each individual capacitor.

Q1 = C1V
Q2 = C2V

Then I know when reconnected, the net charge has to equal the new charge. So:

q1+q2 = Q1-Q2

Then the voltage across them has to be the same. So:

V' = q1/c1 = q2/c2

Then I solved them sim. and got:

q1 + (c2/c1)q1 = Q1 - Q2

But when I plug in my numbers, I get the wrong answer. What am I doing wrong?
 
Last edited:
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  • #2
RavageU said:
Since they are connected in parallel, I found the charge for each individual capacitor.

Q1 = C1V
Q2 = C2V

Now I'm confused about what happens when I reconnect them. Would the voltage (229) across them be the same since they are in parallel?

They are connected in parallel but the way the leads were arranged the voltages are opposing. So current will flow to "even out" the potential.

You might find it convenient to assign charge (coulombs) to each plate before the reconnection, then determine what will remain after the cancellation happens when opposite charges are "introduced" to each other via the new connections.
 
  • #3
Edited for more that I've done to solve the problem.

So the charges essentially cancel out?
 
  • #4
RavageU said:
Edited for more that I've done to solve the problem.

So the charges essentially cancel out?

Some of the charge is going to cancel, because you're connecting the + plate of one cap to the - plate of the other. One capacitor has more charge on it than the other. Figure out what remains.
 
  • #5
So would it be Q1-Q2 (The initial charges of the capacitor) = q1 + q2 (The charges after reconnection)?
 
  • #6
RavageU said:
So would it be Q1-Q2 (The initial charges of the capacitor) = q1 + q2 (The charges after reconnection)?

Sounds good. Now you just need to figure out how that remaining charge will distribute over the caps.
 
  • #7
So because they are parallel, the voltage across the plate have to be the same, so I have:

V' = q1/c1 = q2/c2

and solving simulatenous, I get:

q1 + (c2/c1)q1 = Q1 - Q2

Plug in the numbers, and I get ~3507 which is still the wrong answer...
 
  • #8
Ah, but 3507 what? And how do your significant figures compare with those given as original information?
 

1. How does connecting parallel capacitors to a battery affect the voltage and current?

Connecting parallel capacitors to a battery does not affect the voltage, as the voltage across each capacitor remains the same as the battery voltage. However, the total current drawn from the battery increases, as the capacitors act as individual loads.

2. What is the purpose of connecting parallel capacitors to a battery?

The purpose of connecting parallel capacitors to a battery is to increase the total capacitance in a circuit. This can be useful in applications where a larger capacitance is required, such as in power supplies or audio amplifiers.

3. How do parallel capacitors behave when connected to a battery in a DC circuit?

In a DC circuit, parallel capacitors behave as individual loads, each drawing current from the battery. The capacitors will charge and discharge at different rates depending on their individual capacitances and the circuit resistance.

4. Can parallel capacitors connected to a battery store more charge than a single capacitor?

Yes, parallel capacitors connected to a battery can store more charge than a single capacitor. The total charge stored is the sum of the charges stored in each individual capacitor.

5. Is there a limit to the number of parallel capacitors that can be connected to a battery?

There is no limit to the number of parallel capacitors that can be connected to a battery. However, as more capacitors are added, the total capacitance of the circuit will increase, potentially causing inefficiencies in the circuit and affecting its overall performance.

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