Finding the magnitude of the current across a capacitor

Thread Starter

renee123

Joined Dec 9, 2018
1
Hello! I would like some help with the following circuit.
upload_2018-12-9_19-4-50.png
I am asked to calculate the magnitude of the current across C1. I am suggested to find the total impedance in the circuit and then find the current across C1. I know that the answer should be 31.4A. I don't really know how I should approach this problem. I do not understand if C4 and C2 are in series or parallel. To me it looks like C2 and C4 are in series and in parallel to C1 and C3. I have tried it like this and then applied the mesh method to find I1, but I did not find 31.4A.
Thank you for your help!
 

MrChips

Joined Oct 2, 2009
20,197
Welcome to AAC!

Don't let the schematic diagram fool you.

You say C4 and C2 are in series.
What about C4 and C1?
What about C4 and C3?

What can you say about C1, C2, and C3?
 

BBee

Joined Dec 6, 2018
35
Just a minor point to start with. Currents are measured through things, voltages across.

Hopefully this won't confuse you, but possibly an idea to remember things by: If you look at the capacitor symbol you will see that the capacitors C1 to C3 effectively increase the plate area when coupled across each other so the capacitances add. C4 is in series so the gap in the circuit effectively increases so the total capactance decreases.

Tracy
 

Alec_t

Joined Sep 17, 2013
10,901
Welcome to AAC!
You might want to check whether mF here means microFarad ot milliFarad. Both abbreviations have been used in the past. It's usually clear what is intended from the circuit context, but this is a purely academic problem circuit.
 

BBee

Joined Dec 6, 2018
35
Another analogy you may find useful is to liken current to the flow of water in a river. This flows from the source (generator) and flows through what it comes across (unless it is an insulator). Like a river, at a junction the current splits in proportion (dependent on impedance values). When the tributaries re-join the current re-combines. This being a circuit academic in nature, external effects which may affect this can be dis-regarded.

Tracy
 

WBahn

Joined Mar 31, 2012
25,223
Hello! I would like some help with the following circuit.
View attachment 165443
I am asked to calculate the magnitude of the current across C1. I am suggested to find the total impedance in the circuit and then find the current across C1. I know that the answer should be 31.4A. I don't really know how I should approach this problem. I do not understand if C4 and C2 are in series or parallel. To me it looks like C2 and C4 are in series and in parallel to C1 and C3. I have tried it like this and then applied the mesh method to find I1, but I did not find 31.4A.
Thank you for your help!
C2 and C4 are neither in series nor parallel. To be in series, whatever current flows through one MUST flow through the other. To be in parallel, whatever voltage appears across one MUST appear across the other.

But you DO have some components that ARE either in series or parallel (you need to figure out which ones) and, after combining them into a single effective component, you can then simplify the circuit further.

In order to see things in a way that is probably more natural to you at this stage, replace the capacitors with resistors and then see how you might approach things if asked to find the current through R1. Then switch back to the actual circuit and follow the same steps.
 
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