How is the Time Constant Calculated in an RC Circuit?

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Homework Help Overview

The discussion revolves around calculating the time constant in an RC circuit, specifically focusing on the current through a particular resistor (R3) and the role of other resistors (R1, R2, and R4) in the circuit's behavior.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to clarify whether the resistance used in the time constant formula (RC) should include only R3 or the total resistance of the circuit. Some participants question the influence of other resistors on the current through the capacitor and whether additional resistors would alter the effective resistance in the time constant calculation.

Discussion Status

The discussion is exploring different interpretations of how resistors in the circuit affect the time constant and current. Some participants are beginning to understand the role of the capacitor and its relationship with the resistors, while others are still questioning the assumptions regarding the circuit configuration.

Contextual Notes

Participants are considering the implications of having a closed switch and the potential addition of another resistor (R4) in the circuit, which raises questions about the overall resistance affecting the capacitor's behavior.

theBEAST
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Homework Statement


I attached a picture of the RC circuit. The question asks to find the current as a function of time for light bulb 3 (R3). I know that I=Ioet/RC where Io is the initial current that runs through R3 but what about the R in the time constant RC? Is this resistance the total resistance of the circuit or is it just the resistance in R3?
 

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Do R1 and R2 have any effect on the current through C?
 
technician said:
Do R1 and R2 have any effect on the current through C?

Hmmm no, I think I kind of get it now, so the capacitor only affects anything on the outer loop. So the resistance I would use is just R3 right?

(PS I forgot to mention the the switch is closed)

Now let's say instead of a switch we had an extra resistor R4. Would that mean the R in t=RC would be R3+R4 since the capacitor is affected by both resistors that are in series?
 
technician said:
delete

huh? :O
 

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