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Initially charged capacitor disharged through a resistor

  • Thread starter Mike88
  • Start date
  • #1
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Homework Statement


A capacitor with initial charge q0 is discharged through a resistor.
(a) In terms of the time constant τ, how long is required for the capacitor to lose the first one-third of its charge? answer x tau
(b) How long is required for the capacitor to lose the first two-thirds of its charge?
answer x tau



Homework Equations


i = -(q0/RC)e(-t/RC)


The Attempt at a Solution


I tried solving for time t and got -RC*ln(q/q0)= t
I'm lost i don't know what to do

Homework Statement





Homework Equations





The Attempt at a Solution

 

Answers and Replies

  • #2
Doc Al
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I tried solving for time t and got -RC*ln(q/q0)= t
Looks good to me (except for the minus sign). So what's the time when q = q0/3?
 
  • #3
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Looks good to me (except for the minus sign). So what's the time when q = q0/3?
i then get t = RC*ln(1/3) where RC = tau

is this correct?
 
Last edited:
  • #4
Doc Al
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44,865
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i then get t = RC*ln(1/3) where RC = tau

is this correct?
Yes. But put that minus sign back in. (I didn't see that you had q0 on top! :wink:)
 
  • #5
6
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Yes. But put that minus sign back in. (I didn't see that you had q0 on top! :wink:)
thanks for the help i figured out everything.
 

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