# Find resistance of resistor in RC circuit

## Homework Statement

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.

## Homework Equations

Thevenin's theorem

## 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.

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gneill
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.

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.
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?

gneill
Mentor
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?
Looks like a good deduction:)

Looks like a good deduction:)
Appreciate it, a lot! :)