# Capacitance in Parallel and in Series

1. Mar 23, 2009

### islandboy401

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

In the FIGURE (shown below in "attempt at solution" section), find the equivalent capacitance of the combination. Assume that C1=10 nF; C2 = 5 nF; and C3 = 4 nF.

2. Relevant equations

For parallel capacitors: Ceq = C1 + C2 + C3 +...

For series capacitors:

3. The attempt at a solution

My answer is 4.74 nF though my answer key says 3.16 nF. Am I doing something wrong?
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Mar 23, 2009

### unknown_2

in series : $$\frac{1}{C_{eq}}$$ = $$\frac{1}{C_{1}}$$ + $$\frac{1}{C_{2}}$$ + $$\frac{1}{C_{3}}$$.... etc

in parallel $${C_{eq}$$ = $${C_{1}$$ + $${C_{2}$$ + $${C_{3}$$ ... etc

basically the opposite to resistance

so from your diagram... (C1 // C2) + C3

so it should be $$\frac{1}{C_{eq}}$$ = $$\frac{1}{10 + 5}$$ + $$\frac{1}{4}$$

so $$C_{eq}$$ = 3.16nF

hopefully that helps

3. Mar 23, 2009

### islandboy401

Thanks...I understand what I did wrong.