# Another math ? Capacitance.

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#### daveleonard

##### Member
I am a rank beginner so please have patience with me. "Two capacitors valued at 400 and 600 uf consecutively are connected in series in an electric circuit. What is the value of its equivalent capacitance?
I know the answer is 240 uf but what I need to know is how to figure that. The math involved so I can reasonably answer a test question with different values. Thanks.

#### wx5uif

##### Member
Take the reciprocal of both and add them together. Then get the reciprocal of that number.

1/400 = .0025
1/600 = .00166666667

.0025 + .00166666667 = .004166666667

1/.00416666667 = 240 (well 239.999999 (rounding here...))

#### mikewazowski

Staff member
Forums Manager
400x600 240000
---------- = --------- = 240
400+600. 1000

#### ramal121

##### Lots and lots of watts
400x600 240000
---------- = --------- = 240
400+600. 1000

Mike, you cheat. But that only works for two. Sum of the reciprocals always works with any number of caps in series (or resistance, inductance in parallel).

Last edited:

#### mikewazowski

Staff member
Forums Manager
Well, since he only asked about two, I figured I would give him the fastest way to the answer.

D

#### DaveNF2G

##### Guest
How did the OP know the result without knowing the math?

#### joen7xxx

##### Member
FCC Question Pool?

#### daveleonard

##### Member
NF2G. I knew the answer by taking trial exams but I don't just want to memorize the answers I want to know the math so I can answer the question when posed with different values. Thanks Dave.

#### daveleonard

##### Member
Thanks all. I'll use reciprocal when more than two.

D

#### DaveNF2G

##### Guest
NF2G. I knew the answer by taking trial exams but I don't just want to memorize the answers I want to know the math so I can answer the question when posed with different values. Thanks Dave.

Good for you! We need new hams who actually understand the theory and rules. Keep on asking and learning.

Do any of the ham clubs near you offer licensing classes? Could be a big help if available for you.

#### daveleonard

##### Member
Thanks NF2G, I took my Tech exam on April 5th and feel pretty good about it, will know in a couple of weeks. My XYL wants to take her 2 Meter DY Lic exam in Sept but we need to find an orientation Seminar here in the Philippines. We live on Camiguin Island. Clubs are spread pretty far apart here. I will be only the 2nd ham here on the island.
Thanks again, 73's Dave

#### elk2370bruce

##### Member
Are there reciprocal operating privileges between US and Phillipines? You need to know that before you return to Canmiguin.

#### daveleonard

##### Member
There is a reciprocal between the US and the Philippines but my US lapsed in 2002 because I knew I would be coming to the Phils on a permanent basis and didn't know about the reciprocal. So now I have to start over, trying to remember all the stuff I forgot, with the tech license and then later in the summer the general license. The Philippines still has a beginner license called the DY license just for 2 meters, kinda like the old Novice Lic in the States. I should not have let my US lic expire but I needed a refresher anyway. The exams are pretty much the same except for a few rules and freq differences. The theory is all the same, never changes.

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