# determine the polarity of capacitors

#### gbox

Joined Dec 29, 2015
42

How do I determine the polarity of capacitors?

My attempt:

Last edited:

#### Alec_t

Joined Sep 17, 2013
11,814
Bearing in mind this is your homework, what are your thoughts so far?

#### Papabravo

Joined Feb 24, 2006
14,880
Not all capacitors have polarity as an intrinsic property. Certain types do have an associated polarity, namely electrolytic and tantalum capacitors. If the schematic symbol does not indicate a polarity, then you can work on the assumption that any of the given capacitors could have either a positive or negative voltage, if the sources were ac sources, which they are not. Your schematic has no DC current paths. Where did you get this problem?

#### WBahn

Joined Mar 31, 2012
26,398

How do I determine the polarity of capacitors?
When will you get the hint that you are expected to show YOUR best attempt to solve YOUR homework problems instead of just asking others to work them for you (or to tell you how to work them)?

Future threads that you start in which you do not show some kind of honest attempt will be locked and/or deleted.

#### gbox

Joined Dec 29, 2015
42
sorry, edited

#### WBahn

Joined Mar 31, 2012
26,398
What is you reasoning for each of these? How are we to know that these aren't just random guesses?

#### gbox

Joined Dec 29, 2015
42
I started with the left $$8V$$ battery and took the left side of C1 to be + and than the right side - and so on

#### WBahn

Joined Mar 31, 2012
26,398
I started with the left $$8V$$ battery and took the left side of C1 to be + and than the right side - and so on
So would you have gotten the same results if you had started on the right side?

If not, does it seem reasonable that the polarity of the capacitors (by which I am assuming you mean the polarity of the charge stored on the capacitors) depends on which end you start with?

How about analyzing the circuit and determining what the charge is on each capacitor. Won't that tell you the polarity of each?

#### gbox

Joined Dec 29, 2015
42
No I get 2 different answers if I look first at the right voltage source or on the left voltage source

#### hp1729

Joined Nov 23, 2015
2,304

How do I determine the polarity of capacitors?

My attempt:

Do we assume all capacitors are the same type and value? Would it make a difference?

#### crutschow

Joined Mar 14, 2008
26,067
Assuming you start with discharged capacitors and then apply the voltages, the relative capacitor voltage and polarities will depend upon the relative capacitance value of each capacitor.
So you need to write node voltage equations for all the nodes that include the capacitor values as variables to solve the problem.

#### WBahn

Joined Mar 31, 2012
26,398
Do we assume all capacitors are the same type and value? Would it make a difference?
Not so much same type (e.g., mylar vs. ceramic), though the leakage will impact the final distribution and we can only assume negligible leakage.

The relative values will affect the polarity of the charge on a couple of them. An interesting more advanced exercise is to identity those capacitors for which the polarity is known regardless of the values of any of the capacitors.