Year 12s: what will be the first way you research your future options? >>

Capacitance, Voltage and Time Constant Question

2.2x10^-3F Capacitor charged with a 12V battery. It is then discharged through a 10k(ohms) resistor.

So the voltage I'm given is 12V the time constant is 22s. I'm asked what will the voltage be across the capacitor after 22s? Does anyone know the answer?

Reply 1

NatKH

Nevermind I found the answer. I used V = V(0)e^-(t/RC) equation to get 4.41V.

Reply 2

Joinedup

Original post by NatKH

Nevermind I found the answer. I used V = V(0)e^-(t/RC) equation to get 4.41V.

FWLIW The rule of thumb is that it decays by 63 (ish) % after one time constant... or decays to 37 (ish) % of it's original value.

Of course the equation will give you an answer even when the time elapsed isn't a whole number of time constants.