A Capacitor with initial charge

[Onur]

Homework Statement

A capacitor with initial charge q0 is discharged through a resistor. What multiple of the time constant τ gives the time the capacitor takes to lose

(a) the first 1/8-th of its charge
(b) 7/8-th of its charge?

Homework Equations

The Attempt at a Solution

since ı know q0.e-t/rc but ı could not do it

 

[berkeman]

Homework Statement

A capacitor with initial charge q0 is discharged through a resistor. What multiple of the time constant τ gives the time the capacitor takes to lose

Homework Equations

(a) the first 1/8-th of its charge
(b)7/8-th of its charge?

The Attempt at a Solution

since ı know q0.e-t/rc but ı could not do it

Welcome to the PF.

Just set up those exponential equations and solve for time. Do you know how to take the natural log of both sides of an exponential equation to be able to pull the time variable out of the exponential?

 

[Onur]

Welcome to the PF.

Just set up those exponential equations and solve for time. Do you know how to take the natural log of both sides of an exponential equation to be able to pull the time variable out of the exponential?

no i don't know

 

[berkeman]

no i don't know

I'm pretty sure they have been covered in your class, and here is a simple refresher for you:

http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

EDIT -- that link is to the general Hyperphysics page, not the HyperMath page I wanted.

Here is a similar link at Wikipedia -- https://en.wikipedia.org/wiki/Natural_logarithm