A 1.5 uF capacitor is connected in series to a 1.4 uF capacitor. The two are fur

Question

A 1.5 uF capacitor is connected in series to a 1.4 uF capacitor. The two are further connected to a 13.6 Volts non-ideal battery through a 7.1 M resistor. All connections are in series. The internal resistance of the battery is 8.2 m. Both capacitors are initially discharged.

The switch is closed at t=0 s. Find the current in the circuit at t=1.5 seconds.

Note: the current in the circuit after a few seconds is likely to be very small. It is likely that just putting the numbers into a calculator may give you zero, which will not be the acceptable answer. Calculate the result in nA instead.

Explanation / Answer

Ceq = 1.5*1.4 / (1.5 + 1.4)

Ceq = 0.724 micro F

R = r + R

Rnet = 8.2 x 10^-3 + 7.1 x 10^6

time constant = RC = 5.14s

I = Ioe^-t/RC

Io =V/Rnet

Io = 1.915 x 10^-6 A

I = Io*(e^-1.5/5.14)

I = 1.43 x 10^-6 A

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