Finding potential at a point in capacitor

AI Thread Summary
The discussion focuses on calculating voltage at specific points in a circuit involving capacitors and resistors. The current at point a was determined to be 1.82 A using Kirchhoff's law, leading to a query about which resistance value (4.4Ω or 8.8Ω) to use in Ohm's law for voltage calculation. For point b, the potential is being calculated using the charge and capacitance, raising the question of whether to use 0.48 µF or 0.36 µF. Clarifications indicate that either resistor or capacitor value can be used, and the potential at the positive terminal of the source is also discussed. Understanding the potential divider concept is emphasized as relevant to both resistors and capacitors.
Sunwoo Bae
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Homework Statement
shown below
Relevant Equations
Ohm's law, Kirchhoff law,
1644237234303.png


I tried solving the part (a), and got I =1.82 A for the current value using Kirchoff's law.
Next, I want to use Ohm's law to calculate the voltage at point a.
Va = IR
In this equation, will resistance R correspond to 4.4Ω or 8.8Ω?
How do you determine which resistance to use when solving this problem?

As for part B, I was able to calculate Ceq and Q through following works:
1644242333552.png


I am now trying to find the potential at point b with the switch open through equation
Vb = Q/c
Again, which value of capacitance, 0.48 µF or 0.36 µF, and why?

Thank you!
 
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Have you come across the idea of a potential divider? The voltage across either resistors is in proportion to the value of the resistance. The same idea carries across for the capacitors, except the weights are the reciprocals ##1/C##. Can you show why this is true?
 
Sunwoo Bae said:
Homework Statement:: shown below
Relevant Equations:: Ohm's law, Kirchhoff law,

View attachment 296733

I tried solving the part (a), and got I =1.82 A for the current value using Kirchoff's law.
Next, I want to use Ohm's law to calculate the voltage at point a.
Va = IR
In this equation, will resistance R correspond to 4.4Ω or 8.8Ω?
How do you determine which resistance to use when solving this problem?

As for part B, I was able to calculate Ceq and Q through following works:
View attachment 296735

I am now trying to find the potential at point b with the switch open through equation
Vb = Q/c
Again, which value of capacitance, 0.48 µF or 0.36 µF, and why?

Thank you!
You can use either resistor value.

You can use either capacitor value.

The problem states to use a potential value of 0 V at the negative terminal of the source.
What is the potential value at the positive terminal?
 
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