Homework Help: Solving an RC circuit

1. Jul 14, 2012

T.smriti

Hey,
Actually I am working on my research project and facing a problem on solving a simple series RC circuit. But the problem is the Resistance and capacitance of the circuit is increasing with the time, and I am working on finding the value of R and C at the steady state as well as the time switch is closed(t=0). These two values are obviously going to be different as both R and C are increasing with time.
All information I have about the problem in I have the value of DC input voltage and the current waveform
Also I am working on the charging side of the problem.
I would be highly obliged if anybody could give me some hint or help.

Thanks

2. Jul 14, 2012

CWatters

How fast are R and C are increasing? If much slower than the RC time constant just work out the circuit response at several points in time.

In the real world the manufacturing tollerance on R and C can vary anyway. For R it mught 0.5-2%. For C it could be anywhere from <1% to 80% depending on the type of capacitor. Some types of capacitors also age.

3. Jul 14, 2012

CWatters

If it's the classic Battery -> switch -> R -> C circuit and the switch is closed at t=0 then

At t=0 the voltage on the capacitor is zero and that does not change with R or C. The current will be I=V/R and that _will_ change with R but not C.

At t=infinity, The voltage on the capacitor will equal the supply voltage which is independant of R or C. The current will be zero which is also independant of R or C.