Solution: When t=0-, the capacitor is equivalent to an open circuit, the voltage across the capacitor is 6kω, and UC (0-) = (10/1000) × 6×1000 = 60 (v).

According to the switching theorem, Uc(0+)=Uc(0-)=60V. The equivalent circuit at t=0+ is as follows:

I 1(0+)= 60/(3+3∨6)= 12(mA).

When t=∞, the capacitor is completely discharged, so Uc(∞)=0 and i 1(∞)=0.

The Thevenin equivalent resistance of the circuit is obtained from capacitor disconnection: r = 3+3∑6 = 5(kω).

So the time constant of the circuit is: τ = RC = 5×1000× 2/1000000 = 0.01(s).

f(t)=f(∞)+[f(0+)-f(∞)]e^(-t/τ)。

uc(t)=0+(60-0)e^(-t/0.0 1)=60e^(- 100t)？ ㈤.

i 1(t)=0+( 12-0)e^(-t/0.0 1)= 12e^(- 100t)(ma)。