The figure above shows a circuit containing an electromotive force (a battery), a capacitor with a capacitance of C farads (F), and a resistor with a resistance of R ohms (Ω). The voltage drop across the capacitor is Q/C, where Q is the charge (in coulombs). So in this case, Kirchhoff's Law gives:
RI + Q/C = E(t)
Since the current is I = dQ/dt, we have:
R(dQ/dt) + (1/C)Q = E(t)
Suppose the resistance is 20 Ω, the capacitance is 0.1 F, and the battery gives a constant voltage of E(t) = 30V. Also, the initial charge is Q(0) = 0C. Find the charge and the current at time t.
Q(t) =
I(t) =