Physics
posted by Julie Calder .
A 2.0 micro farad capacitor in a circuit in series with a resistor of .0 MOhms is charged witha 6.0V battery. How long would it take to charge to 3/4 of its maximum voltage?

that was 1.0 MOhms

RC time constant: 2E6*1E=6=2seconds
V=Vo (1e^(t/RC))
with a little math,
.25=e^t/rc
take the ln of each side..
ln(.25) * RC=t
2ln(.25)=t
t=2.77 seconds check that