Calculating Capacitance: Series vs Parallel

[cupid.callin]

Hi all,

This question was given in my physics book. Given that: C1 = 4uF and C2 = 6uF (u=micro) ... it comes out to be C1 + C2 = 10uF

I used the general method ... you know ... assign charges, assume potentials... solve equations.

My question is that aren't the two capacitors highlighted red in parallel, because i guess they are as the potential drop across them is same, but it doesn't work to get the answer i.e. 10uF.

If they are not in parallel, please tell me how to tell if two capacitors are in series or parallel ...

Thanks for help!

 

[gneill]

All the C1s are paralleled by C2s as you spotted. There are four such parallel capacitor instances in the given circuit. They can each be replaced with an equivalent capacitance. This reduces the equivalent circuit to four capacitors, all of the same size. There will be two pairs of series-connected capacitors, which are in turn connected in parallel. The series connected pairs can each be reduced to single equivalent capacitors. Then you're left with these two single capacitors in parallel, so rinse, repeat. You're left with one equivalent capacitor.

The result, 10uF for the equivalent capacitance of the whole circuit, is correct.

 

[cupid.callin]

Oh yes,,, you are right!

I don't know what i was thinking while solving the ques. myself!
More sleep!

One more ques.
Two (or more) capacitors are in parallel if the potential drop across them is same ... Right? Or is there any other way to tell if two are in series or parallel ??!

 

[gneill]

Oh yes,,, you are right!

I don't know what i was thinking while solving the ques. myself!
More sleep!

One more ques.
Two (or more) capacitors are in parallel if the potential drop across them is same ... Right? Or is there any other way to tell if two are in series or parallel ??!

Component terminals need to be physically wired together (the same nodes in a circuit diagram) in order to be in parallel. Two capacitors charged to the same voltage but not connected are not in parallel.

 

[cupid.callin]

Thanks for your help gneill !