Thevanin equivalent circuit SOLVED

I'm stuck on a question and I was wondering if somebody could help. This is supposed to be one Thevanin equivalent circuit, tested in two different ways. The measured current is shown in the diagram.

I am having trouble figuring out how the current in the first test can be 0?

by bmathre
November 14, 2016

1 Answer

Answer by hevans

Hi @bmarthe, This is a great question!

Whenever doing thevanin equivalent problems I always like to draw the circuit out to see what I'm dealing with.

Looking at this you can start to get an idea of how to answer your first question. The logic kind of goes like this:

  1. If 0 amps are going through R1, that means that 0 ams also going through R2.
  2. If no current is flowing through R1 + R2, then no voltage is dropped across those resistors.
  3. If no voltage is dropped across R1 + R2, then the positive terminal of $V_{th}$ has to be 10V.

So if we fill in these values, and check out your second test case, we have this

Looking at the picture, we can make the following observations

  1. 5 mA must be going through $R_{th}$
  2. 10V must be dropped across $R_{th}$

So from there its just a matter of plugging into

$$V = IR$$ $$10V = 5mA \times R_{th}$$ $$R_{th} = \frac{10V}{5mA}$$ $$R_{th} = 2 \Omega$$

ACCEPTED +1 vote
by hevans
November 15, 2016

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