RC circuit and a microfarad capacitor

[lha08]

Homework Statement

A 10.0 microfarad capacitor is charged by a 10.0 V battery through a resistance R. The capacitor reaches a potential difference of 4.00 V in a time interval of 3.00 s after charging begins. Find R.

Homework Equations

The Attempt at a Solution

So basically i got an answer of 587314 ohms..which is kinda a large number...but i don't know the right answer. So what I did was that i used the formula: emf - potential difference capacitor - IR = 0. Then i plugged in the values for the emf and the p.d. capacitor, which gave me 6. Then for the IR part, i plugged in the current as a function of time formula for charging in the 'I' spot and then simply plugged in the R value from the data. Then after calculating, I 'ln' both sides and solved for R...to me, it makes sense, but that's just me..could anyone help me confirm whether the steps I'm doing is correct or even better if they got the same answer as me...??

 

[ehild]

Show your calculations in detail. What formula did you use for the time-dependence of the current? By the way, your result is correct. A resistor of a few hundred kilo-ohm is quite common.

ehild