A simple series R-C circuit in a defibrillator has capacitance C = 25 millifarad and effective resistance R = 4 ohm. The capacitor is fully charged.

Then, at t = 0 s, the defibrillator is activated, so essentially a switch is closed allowing current to flow through the resistance and capacitor.

At t = 0.5 s, what fraction (approximately) of the total stored charge, has flowed from the capacitor?

Select one:

a. 99%

b. 63%

c. 80%

d. 33%

e. 10%

I've used I=dQ/dt and it has given me 0.05A but I don't know where to go from here, am I on the right track?