The capacitor in an RC circuit has a capacitance of 25.8 µF.
(a) If the time constant for this circuit is to be 2.7 ms, what should be the resistance?

I got 105 ohms which is correct.

(b) If the capacitor is initially uncharged, what is the charge on the capacitor 5.6 ms after it is connected to a 8.0 V battery? (Give your answer in µC.)

Question

The capacitor in an RC circuit has a capacitance of 25.8 µF.
(a) If the time constant for this circuit is to be 2.7 ms, what should be the resistance?
  
I got 105 ohms which is correct.

(b) If the capacitor is initially uncharged, what is the charge on the capacitor 5.6 ms after it is connected to a 8.0 V battery? (Give your answer in µC.)

kropot72 · Answer

Your answer for part (a) is correct to the nearest ohm.
The equation for the charge on the capacitor after time t is:
$$\large q=CV (1-e^{-\frac{t}{CR}})$$