For the circuit shown (Fig. 19-11), a 40-μF capacitor is added across the 20-μF capacitor in the circuit of Fig. 19-10. Find the time constant of this circuit and the voltage across this circuit 3 s after the start of charge.
Find the total capacitance for two capacitors in parallel.
Parallel: C_T=C_1+C_2=20+40=60\ \mu F
Then T=R C_T=\left(100 \times 10^3\right)\left(60 \times 10^{-6}\right)=6\ s
Write the formula for charging voltage and substitute values to find v_{C}.
v_C=V\left(1-e^{-t / R C}\right) (19-17)
=10\left(1-e^{-3 / 6}\right)=10\left(1-e^{-0.5}\right)=10(1-0.607)=10(0.393)=3.93\ V