Hi

While solving problems related to RC circuit, I'm having problem finding Thevenin equivalent resistance across the terminals of a capacitor. Please have a look on the attachment. It has my question there. Please help me with it. Thanks a lot.

 

hey, only took me a page and a half for 4 different Thevenin equivalents (TE) to work this out, and thus I don't trust my work until I do it again on a clean sheet and get the same answers. But here it is and you can get the general scheme I used.

First I split the circuit up at A&B into 3 pieces: Vs R1 R2, C, and R3 R4 R5. Leave C alone and solve the left & right side TE's 1&2.

Now jam the left & right side TE's 1&2 together and find THAT resultant TE3.

You now have a nice single source, single R and single C. Solve for how C charges Vcap.

Now go back to the right side TE and break it up to look back from R4. Note here the C cap is the source and we treat it like any other source: we short it for the analysis.

That TE gives you how the Io changes given the cap voltage Vcap. But we already found Vcap, so it is a simple substitution to find the current.