# Homework Help: Find resistance of resistor in RC circuit

1. Dec 25, 2014

### AndrejN96

1. The problem statement, all variables and given/known data
Find the resistance of resistor R7 when the switch is turned on so that the power of that resistor is maximum in the circuit.

The voltage of the capacitor before the switch is turned on is Vc=200V.

2. Relevant equations
Thevenin's theorem

3. The attempt at a solution
I believe I should be using Thevenin's theorem but I have no idea how to put it. Help would be appreciated.

2. Dec 25, 2014

### Staff: Mentor

It looks like you should be first trying to determine the value of E3. Do this before the switch is closed.

Pay close attention to the role of $I_s$: it renders the effects of several other components to be nil.

At steady state the capacitor "looks like" an open circuit, so you need to find E3 such that the voltage across the place where C connects is 200 V. The current $I_s$ plays an important role here.

3. Dec 25, 2014

### AndrejN96

So is Is going to flow through R3 and Vc is going to be equal to E3-Is*R3, and I find E3 from there?

4. Dec 25, 2014

### Staff: Mentor

Looks like a good deduction:)

5. Dec 25, 2014

### AndrejN96

Appreciate it, a lot! :)