Time taken to charge capacitor to 2/3 V in

[mogley76]

Homework Statement

C= 0.047 micro farads
R= 2.2K
using the formula given, calcultae the time taken to charge the capacitor to 2/3 V in.

Homework Equations

Vc = Vin * (1-e^-t/rc)

The Attempt at a Solution

rc= 2.2E3 * 0.047 E-6 = 1.034E-4 seconds ( 1 time constant , 63% of vin )

i can't figure out figure out after that, i know 1 time constant is 63% and 2/3 is slightly higher than that around 67% of vin but how do i work out the time taken to reach that?

 

[gneill]

You should be able to solve the equation for t.

 

[mogley76]

t = -rc* ln(1-vc/vn)

got it thanks