Capacitors won\'t hold a charge indefinitely; as time goes on, charge gradually
ID: 1421188 • Letter: C
Question
Capacitors won't hold a charge indefinitely; as time goes on, charge gradually migrates from the positive to the negative plate. We can model this as a discharge of the capacitor through an internal "leakage resistance." A 0.50 F capacitor charged to 2.8 V will initially discharge with a leakage current of 0.30 mA .
Part A:
What is the leakage resistance?
Express your answer to two significant figures and include the appropriate units.
PART B:
How long will it take for the capacitor voltage to drop to 1.0 V?
Express your answer to two significant figures and include the appropriate units.
Explanation / Answer
a) leakage Resistance = V/I = 2.8 / 0.3 = 9.3 k-ohm
b) leakage resistance does not change with voltage
Voltage on discharging
V = Vo*e^(-t/RC)
1 = 2.8 *e^(-t/9333.3*0.5)
t = 4804.88 s