RC Circuit find capacitor charge

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Homework Help Overview

The discussion revolves around an RC circuit problem involving a capacitor that is initially uncharged. Participants are tasked with finding the charge on the capacitor and the current in the circuit after one time constant when connected to a 9.0-V battery.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants express uncertainty regarding the equations to use, particularly questioning the correct form of the charge equation and the meaning of the initial charge (qo). Some suggest using the maximum charge formula, while others discuss the relationship between current and charge over time.

Discussion Status

There are various attempts to clarify the equations and relationships involved in the problem. Some participants have made progress on the first part of the problem, while others are grappling with the second part and expressing confusion about their calculations. Guidance has been offered regarding the use of specific formulas, but no consensus has been reached on the correct approach.

Contextual Notes

Participants are working under the constraints of the problem statement, which specifies the values for resistance and capacitance, and the initial conditions of the circuit. There is ongoing discussion about the definitions and assumptions related to the variables involved.

matt72lsu
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Homework Statement


The capacitor in an RC circuit (R = 130 \Omega, C = 40uF) is initially uncharged.
1) Find the charge on the capacitor in the circuit one time constant (tau = RC) after the circuit is connected to a 9.0- V battery.
2) Find the current in the circuit one time constant (\tau = RC) after the circuit is connected to a 9.0-V battery.

Homework Equations


R = V/I
Q = qo[1-e^-t(RC)] ?


The Attempt at a Solution


Im actually not sure I even have the correct equations and I'm not sure what to use for qo
 
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matt72lsu said:

Homework Statement


The capacitor in an RC circuit (R = 130 \Omega, C = 40uF) is initially uncharged.

Homework Equations


R = V/I
Q = qo[1-e^-t(RC)] ? not correct


The Attempt at a Solution


Im actually not sure I even have the correct equations and I'm not sure what to use for qo


Q=qo[1-e^(-t/(RC))]

ehild
 
matt72lsu said:
R = V/I
Q = qo[1-e^-t(RC)] ?

Im actually not sure I even have the correct equations and I'm not sure what to use for qo

Qo=C*V
 
I'm so confused
 
In the problem C and V is given. When the capacity is fully charged, the maximum charge Qo = C*V. Find this one.
In the relevant equation, put t = RC and find Q.
 
i got the first part but i got the second part wrong. i did V/R = 6.9e-2. then i multiplied that by 1-e^-1 and got 4.4e-2 then multiplied that by 1000 to go from A to mA and got 44. where did i go wrong?
 
There is a similar formula to the Q=qo[1-e^(-t/(RC))] for I(ntensity). It is a must have.
 
yeah I used that and substituted qo for V/R and worked it out the same way i did the first one
 
The current I = dQ/dt = (qo/RC)[1-e^(-t/(RC))]
Now find the current.
 
  • #10
i can't wrap my mind around this !
 
  • #11
matt72lsu said:
i can't wrap my mind around this !
The current I = dQ/dt = (qo/RC)[e^(-t/(RC))]
Now find the current.
 

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