Step Response Problem

Thread Starter


Joined Sep 17, 2012
Circuit Problem

My work I have shown on two different images
Work of Problem Part 1

Work of Problem Part 2

Sorry the images are sideways. I just noticed that right after i posted them on ImageShack

The right answer is -2.70 mA and I have -1.50 mA

Am I working the process correctly?

So part 1 I found that the voltage of the capacitor is -9.9V at t=0^- since it is a open circuit voltage since Switch A was closed for a long time and Switch B was open for a long time before t=0

Part 2 I used an integral to find the voltage which I have a feeling is the part where i messed up for t=0^+ in order to find the initial voltage at t=100[ms] in order to find the function of voltage for t>=100[ms]

For part 3 which is the second picture, I used the formula to find capacitor V(t)= Steady State Voltage + (Initial Voltage (V(200[ms]) - Steady State Voltage)e^(t-t_intial)/τ [V] for t>=100[ms] and τ=CR_thevinin
So I found Thevinin Resistance to find τ (Time constant)

I feel besides part two that everything is sound but I have no idea.

Thank you for the help