*** Hooking up a single capacitor So COnFusEd ***

[jfiliaul]

Ok, this maybe a very silly question but I cant find the answer. What is the difference between hooking up a capacitor inline (in series) with the positive line in a circuit and hooking it up in parallel (one side on negative line and one on positive)? It sounds like a real dumb question to me but I have seen it done both ways and Im sure there are reasons why to do it each way but can anyone help shed the light on this for me?

Example: Here is an RC circuit

Negative side --------------------------------\
                                     |                        /
                                     |                       \
                                   cap                 resistor
                                     |                       /
Positive side --------------------------------\

VS

Negative side --------------------------------\
                                                              /
                                                              \
                                                       resistor
                                                              /
Positive side ----------|---cap----|---------\



THANKS FOR THE HELP !!! 

[Ian]

hi
the first one looks correct to me. that is the way they are normally hooked up

[w2aew]

It depends entirely on the application.

The parallel combination can be considered a low-pass filter.  It's a typical configuration for filtering a power supply for example.  It allows DC to flow through the resistor, and shunts AC away from the resistor.  The higher the frequency, the more that is shunted.

The series combination can be considered a high-pass filter.  It blocks DC from passing through the resistor.  Thus, the impedance of the circuit is very high (infinite) at DC, and drops as the frequency increases.

The answer is - both are correct.  Each of these configurations are used for different purposes.

[Tony R]

Look at how they will act in DC conditions... if your application is DC...

in parallel the cap will act as a open circuit (no current will go though it) so you basically just have a resistor.

in series, the cap will still act as an open circuit, so what happens with the current?

for AC condtions we can kind of think the same way, what is a DC condition, essentially a very slow AC signal (where the period extends to infinity.) so with them in parallel, the current will tend to go though the resistor, in high frequencys, they will tend to go though the cap (acting as a short)