P 8.6-8 Determine v_c(t) for t > 0 for the circuit of Figure P 8.6-8.

Figure P 8.6-8

Assuming circuit is in steady-state prior to t = 0, we have the following with annotations

Since the capacitor is acting as an open circuit, the voltage v_C is the same as the output voltage of the op-amp. So we can find that by calculating the two currents indicated. We know the voltage at point labeles, v_A must be zero since the non-inverting input is grounded and the rules of op-amps require the two inputs be at the same voltage.

Solving for v_C

After the time t = 0, the voltage supply becomes active and the steady-state circuit becomes

Again, v_A remains at 0 V. i₁ is no longer zero.

So i₂ becomes

Solving for v_C

Since the op-amp acts like a current source the Thevenin resistance is 4 kΩ, so plugging into the standard formula gives us

Dr. Donovan's Classes Page	Dr. Donovan's PH 320 Homework Page	PH 320 Homework Chapter 8 Page
Dr. Donovan's Main Web Page	NMU Physics Department Web Page	NMU Main Page

Please send any comments or questions about this page to ddonovan@nmu.edu

This page last updated on July 17, 2019