Electric Circuit Question PLEASE HELP

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Homework Help Overview

The problem involves an electric circuit with a capacitor and resistors, where the capacitor is initially uncharged. The inquiry focuses on determining the current through each resistor at two distinct time points: immediately after the switch is closed and after a long period has passed.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the arrangement of the circuit components and clarify the specific questions being asked regarding current through the resistors at different times.

Discussion Status

There is an ongoing exploration of the implications of the capacitor's behavior at t = 0 and t = infinity, with some participants providing insights into how the circuit behaves under these conditions. Guidance has been offered regarding the interpretation of the circuit at these two time points.

Contextual Notes

Participants are referencing a visual representation of the circuit, which is crucial for understanding the problem setup. There is a focus on the distinction between current through the capacitor and current through the resistors, highlighting the need for clarity in the problem statement.

vortex193
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Homework Statement


20fyjkn.jpg


V = 1.2 kV
C = 65 micro Farads
R1 = R2 = R3 = 0.75 MegaOhms

With C uncharged, switch S is closed (t = 0). At t = 0, what is the current through each resistor? At t = infinity, what is the current through each resistor?

Homework Equations



V= IR
q = qo[1 - e^-t(RC)] (charging of capacitor
q = qoe^-t/(RC)] (discharging of capacitor)

The Attempt at a Solution


Homework Statement


Homework Equations


The Attempt at a Solution

 
Last edited:
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umm... how exactly are those components arranged and what is the problem asking you to find?
 
sorry guys. the question is:
With C uncharged, switch S is closed (t = 0). At t = 0, what is the current through each resistor? At t = infinity, what is the current through each resistor?
 
xcvxcvvc said:
umm... how exactly are those components arranged and what is the problem asking you to find?

do you see the picture? if not here is the link:
http://tinypic.com/r/20fyjkn/6
 
vortex193 said:
do you see the picture? if not here is the link:
http://tinypic.com/r/20fyjkn/6

At t = 0, an uncharged capacitor has zero charge on it and zero voltage drop across it. At t = infinity, a capacitor's plates are fully charged and have no current going "through" them.
 
xcvxcvvc said:
At t = 0, an uncharged capacitor has zero charge on it and zero voltage drop across it. At t = infinity, a capacitor's plates are fully charged and have no current going "through" them.

but its not asking for the current through the capacitor but the current through the resistor
 
At t=0 the circuit is equivalent to a circuit with C replaced by a wire.
At t=infinity the circuit is equivalent to a circuit with C replaced by an open switch.

You should be able to figure out the currents in these resistor only circuits.
 
vortex193 said:
but its not asking for the current through the capacitor but the current through the resistor

Yes, but if it has zero current through it, it looks like an open circuit, and if it has a drop of zero volts, it looks like an short circuit. I was trying to get you to arrive to the answer instead of stating it.
 

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