A 9.0 μF and 4.0 μF capacitors are connected in parallel

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Homework Help Overview

The discussion revolves around a problem involving capacitors, specifically a 9.0 μF and a 4.0 μF capacitor connected in parallel, which is then connected in series with a 12.0 μF capacitor. The original poster expresses confusion regarding the voltage distribution across the capacitors when a voltage is applied to the entire network.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to understand the voltage behavior across capacitors in parallel versus series, questioning their assumptions based on resistor behavior. Other participants provide calculations for equivalent capacitance and voltage across the capacitors, while also discussing the charge distribution in series.

Discussion Status

Participants are exploring different interpretations of the voltage across the capacitors, with some providing calculations and clarifications. The original poster has received helpful explanations that address their confusion, indicating a productive direction in the discussion.

Contextual Notes

The original poster mentions that their textbook does not clearly explain certain concepts, which may contribute to their confusion regarding the problem.

mikebc
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A 9.0 μF and 4.0 μF capacitors are connected in parallel...

Hi, I understand how to do most of this question, I completed "A", but I am confused with question "B". I think that the series capacitor would have full voltage going across it and that the parallel capacitors would have less voltage. But since resistors work oppositely then capacitors and this is the same way to work out resistor voltage I am wondering if I am working it out wrong. Any help would be appreciated.

Question
A 9.0 μF and 4.0 μF capacitors are connected in parallel, and this combination is
connected in series with a 12.0 μF capacitor.
a. What is the net capacitance?
b. If 32 V is applied across the whole network, calculate the voltage
across each capacitor.


I have attached a scan of how I think that it works.

Thanks!
 
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Oops, I forgot to add attachment...

Here is the scan.
 

Attachments

Equivalent capacitance = 6.24 micro F. From Q = CV we get charge Q drawn from the battery = 6.24 x 10^-6 x 32 = 199.68 X 10^-6 C.

When capacitors are in series, the charge on each capacitor is same. 13 micro F capacitor and 12 micro F cap are in series. Hence, Q the charge on each of these is same (199.68 X 10^-6 C).

V = Q/C. Hence voltage across 12 micro F cap = 199.68 X 10^-6/12 x 10^-6 = 16.64 V

Voltage across 13 micro F cap = 199.68 X 10^-6/13 x 10^-6 = 15.36 V

As the voltage across capacitors in parallel is same, voltage across each of 9 & 4 micro F caps will be 15.36 V.
 
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Thank you for explaining that so clearly for me. Some concepts my textbook does not clearly explain, or it is just expected to be understood. Cheers!
 

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