Time for a capacitor to discharge

[joeyjoey]

Homework Statement

A capacitor with an initial charge q0 is discharged through a resistor. In terms of the time constant tau, how long is required for the capacitor to lose the first one-third of its charge?

Relevant Equations

Q(final) = Q(max)e^(-t/RC)
tau = RC
(I have no idea how to use Latex and I apologize)

I already how to properly set it up and execute the equation with natural log etc.

2/3q0 = q0e^(t/RC)
2/3 = e^(-t/tau)
ln(2/3) = -t/tau
t = -ln(2/3)tauThe problem should be trivial; however, -ln(2/3)tau is apparently incorrect. So is ln(3/2). Is there something I am missing?

 

[Delta2]

What you do here seems correct to me, what is the answer key again? Or you don't know it?

 

[joeyjoey]

What you do here seems correct to me, what is the answer key again? Or you don't know it?

I use WebAssign, which has marked it as incorrect. I do not know the answer, but I feel like what I did here is probably right.

 

[haruspex]

I use WebAssign, which has marked it as incorrect. I do not know the answer, but I feel like what I did here is probably right.

Is the required format perfectly clear? E.g. ln(3/2), ln(3/2)tau, ln(3/2)τ, -ln(2/3), 0.4τ, ...

 

[joeyjoey]

Is the required format perfectly clear? E.g. ln(3/2), ln(3/2)tau, ln(3/2)τ, -ln(2/3), 0.4τ, ...

this is how the question looks

 

[haruspex]

View attachment 275953

this is how the question looks

Hmm, ok.
Only other suggestion is to guess a confusion by the question setter and try 1/3 instead of 2/3.

 

[joeyjoey]

Hmm, ok.
Only other suggestion is to guess a confusion by the question setter and try 1/3 instead of 2/3.

ok. thank you for the help!