Thevenin equivalent and maximum power transfer theorem question

Question

I want to find a load resistance's value so that it gets the maximum power transfer, and thus I am using Thevenin's theorem by finding the equivalent circuit's resistance.

By doing so, I got 2929.28 Ω.

The problem is that one of our classmate's claims that the resistance labelled as R4 doesn't have to be taken into account when calculating the equivalent resistance, with no further explanation as to why or how.

The question would be, does that...statement make any sense? Wouldn't all the resistances need to be grouped together in order to get the Thevenin/Norton resistance?

Below is the circuit and my solution:

Thanks!

Answer 1

You are correct. R4 must be taken into account when calculating the Thevenin resistance. The Thevenin resistance is defined as the resistance looking into the circuit from the load terminals. It is clear that R4 is in series with the rest of the circuit. Imagine if R4 was infinite. According to your classmate, it would have no effect on the Thevenin resistance when it is clear that it makes the resistance infinite. Don't rely on your classmates but use the knowledge that you have gained in the classroom. That is why you are there.

Answer 2

@Barry 's answer is correct, R4 is needed.

Just to add on, your classmate may have confused the Rth and Vth methods. For calculating the thevenin voltage, R4 does not affect the result. This is because the load is an open circuit and draws no current. No current through a resistor means that there is no voltage drop,