# Initially charged capacitor disharged through a resistor

## 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?

## 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

## The Attempt at a Solution

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Doc Al
Mentor
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?

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:
Doc Al
Mentor
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! )

Yes. But put that minus sign back in. (I didn't see that you had q0 on top! )
thanks for the help i figured out everything.