Finding the charge on each capacitor

Femme_physics

1. The problem statement, all variables and given/known data

E = 12V
C₁ = 8 [uF]
C₂ = 6.571 [uF]
C₃ = 6 [uF]

Find:
1) C_T
2) Q₁, Q₂, Q₃ on each of the capacitors.

3. The attempt at a solution

C_T was easy. I wasn't sure how to go about finding Q1, Q2 and Q3.

The idea I had was to simply find the voltage across each of them, but that means I have to ohm's law. But I can't use ohm's law with capacitors. If these were resistors I could. But, I don't have a formula that relates voltage, current and capacitance.

I only have Q = VC

Any clues?

rl.bhat

Total charge extract from the cell is Q = C_T*E.
Across C2 potential difference is V = E.
so Q2= V*C2.
In series combination, charge are the same in each capacitor. Hence Q1 = Q3 = Q - Q2.

Femme_physics

Total charge extract from the cell is Q = C_T*E.
Across C2 potential difference is V = E.
so Q2= V*C2.

Really? I wasn't sure if E=V in C2, but come to think about it it makes sense since the flow is uninterrupted.

So far so good. Simple enough. :)

In series combination, charge are the same in each capacitor. Hence Q1 = Q3 = Q - Q2.

A lot more simple than I would've first imagined. .

My thanks!

Ouabache

Quote by Femme_physics

Quote by rl.bhat

In series combination, charge are the same in each capacitor. Hence Q1 = Q3 = Q - Q2.

A lot more simple than I would've first imagined. .

If you would like to more fully appreciate this concept, there is nice visual information here (last diagram on that page): charge on series capacitance; and a discussion on a thread by another PF member here: why do capacitors 'in series' each carry the same charge?

With your embedded image, you've inspired an interesting task to see if I can translate. How about this?

(Net 10) a. The following circuit which includes three capacitors, is connected to a power source E equal 12 Volts.

(Find):
1. The equivalent capacity of the circuit.
2. The electric charge Q1, Q2, Q3, located over each (capacitor) C1, C2, C3 - respectively.

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rl.bhat Recognitions: Homework Help	Total charge extract from the cell is Q = C_TE. Across C2 potential difference is V = E. so Q2= VC2. In series combination, charge are the same in each capacitor. Hence Q1 = Q3 = Q - Q2.