# RC Circuit Analysis

1. Nov 24, 2013

### jendrix

1. The problem statement, all variables and given/known data

Use current equation and find di/dt expression, hence show if initial gradient were maintained the current would be 0 after 1 time constant.

2. Relevant equations

I calculated RC to be 0.5s i=0.02e^-t/0.5

3. The attempt at a solution

I solved di/dt to be

-0.04e^-2t

i'm stuck where to go next though, can anyone help? Thanks :)

2. Nov 24, 2013

### Integral

Staff Emeritus

3. Nov 24, 2013

### jendrix

Sorry I didn't realise it was linked.The initial circuit was an RC circuit with 100v source in series with a 100uf capacitor and 5kohm resistor.I was then tasked with graphing i vs t for the first 3 seconds and drawing it.After 3 seconds i=5*10^-5

The formula for i was given as 0.02e^-2t

Then calculated CR to be 0.5

Then I had to draw a tangent and estimate the gradient which came out at 0.02/-1.1=-0.018

Then came the question that was asked, hope that helps.

4. Nov 25, 2013

### Staff: Mentor

You differentiated to find the general equation for gradient as a function of time? Well, when you need to know the gradient at some time t1 you simply substitute the value of t1 for t in your general equation for gradient.

5. Nov 26, 2013

### jendrix

Thanks, so the gradient would be -0.04, so after 0.5s( one time constant) the current will have dropped by 0.02, so the current will be 0 after one time constant.

Thanks so much for your help. :)