Voltage across resistors in RC circuit

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Homework Help Overview

The discussion revolves around calculating the voltage, current, and power across two resistors in an RC circuit during a charging and discharging process. The original poster expresses uncertainty about the relationship between the capacitor voltage and the voltage across each resistor over time.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to determine the voltage across each resistor by relating it to the capacitor voltage at specific times, questioning if they are the same. Some participants clarify that the resistors are connected alternately to the capacitor, leading to different voltage readings. There is also discussion about calculating the time constant and the need to visualize the circuit more clearly.

Discussion Status

Participants are actively engaging with the problem, providing clarifications about the circuit setup and suggesting that the original poster reconsider their understanding of the connections. There is acknowledgment of the need to use the graph for further insights, but no consensus has been reached on the calculations.

Contextual Notes

The original poster mentions feeling unconfident in their understanding of the textbook material, indicating a potential gap in knowledge that is being explored through the discussion.

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Homework Statement


Calculate the voltage, current, and power across the two resistors for every second of run 1 in the RC circuit.

The RC Circuit:
694ck0.png


The settings of the circuit:
r8xqhe.png


The Graph. The capacitor is charged until it reaches 5.0 V and then discharged until it reaches 1.0 V. This process occurs four times total.
v5czvb.png


Homework Equations


VC = ξ * (1 - e-t/RC)
(Not sure about others.)

The Attempt at a Solution


This is a lab more so than a question and therefore doesn't necessarily have an exact answer. I am having trouble with the process of getting an answer.

I have eyeballed the voltages from the graph for every second but am unsure how to calculate the voltage across each resistor. Is the voltage in each resistor the same as the voltage that is currently in the capacitor at time that time s?

I tried calculating the time constant by plugging the capacitor voltage at 5 seconds with a emf of 6.0 V and got 2.79 seconds, but 63% of 6.0 V is 3.78 V and eyeballing the graph I get approx. 2 seconds to reach 63% max voltage.

I feel like I am overthinking this and am unconfident in my knowledge of this section in my textbook, but rereading isn't helping me either.
 
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...am unsure how to calculate the voltage across each resistor. Is the voltage in each resistor the same as the voltage that is currently in the capacitor at time that time s?
No.
The each resistor is connected to the capacitor alternately (A-B-A-...) - so one resistor will have zero volts while the other has some non-zero voltage.
The voltage across the resistor and that of the capacitor, when they are connected, must add up to something.

I tried calculating the time constant by plugging the capacitor voltage at 5 seconds with a emf of 6.0 V and got 2.79 seconds, but 63% of 6.0 V is 3.78 V and eyeballing the graph I get approx. 2 seconds to reach 63% max voltage.
... the time constant is RC=2secs. Don't know what you were doing.

I feel like I am overthinking this and am unconfident in my knowledge of this section in my textbook, but rereading isn't helping me either.
You need to take another look at the circuit - maybe redrawing it to separate the charging and discharging stages - leaving out the components that do not contribute. It should become clear.
 
Simon Bridge said:
No.
The each resistor is connected to the capacitor alternately (A-B-A-...) - so one resistor will have zero volts while the other has some non-zero voltage.
The voltage across the resistor and that of the capacitor, when they are connected, must add up to something.

... the time constant is RC=2secs. Don't know what you were doing.

You need to take another look at the circuit - maybe redrawing it to separate the charging and discharging stages - leaving out the components that do not contribute. It should become clear.

Thanks, I was looking at the circuit wrong (I thought the charge was coming out the top and hitting the resistor after the capacitor).

Is there a way to calculate the voltage of the capacitor as it is discharging from 5V?
 
Thanks, I was looking at the circuit wrong (I thought the charge was coming out the top and hitting the resistor after the capacitor).
... it doesn't matter which order the current reaches the capacitor and the resistor.

Is there a way to calculate the voltage of the capacitor as it is discharging from 5V?
... yes, and you should have the equation in your course notes.
However - you should use the graph.
 

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