Ah, your story using R1, R2 network make things a little bit clear. You remind me of Bob Duhamel's video using a ruler with a lady. I don't exactly understand his story. But with your story together, I am progress a little bit forward. I am very slowly reading the Wiki article on uA741 to refresh my memory on old things, at the same time relearning some new things, such the the "Hybrid T small signal model of BJT" which I did not know what is going on when the teacher talks about it, ... :(

Ah, your WikiBook discussion is very good in explaining your basic Voltage and Current ideas, as a background of understanding the opAmp virtual ground concept. As I said, I am refreshing my memory and relearning things I did not understand in college, when studying my rusty EE diploma, in Hongkong Technical Collage. I need some time to warm up.

Here is an attractive movie about the "living voltage diagram" - photos.app.goo.gl/RQyK1DwSPnWLCcnz5... a very sophisticated experiment...

And here is the explanatory text from the WB story above: "Software. Now let's start a program that can visualize the voltage diagram on the screen as a "living" animation. For this purpose, the program make computer "interest" in the local voltages in three key points - the left resistor's end point, the slider intermediate point and the right end point...

... Let's then satisfy its curiosity:) by connecting, for a start, the DAC1's output to the ADC1's input and the DAC2's output to the ADC2's input; then, connect the ADC3's input to the slider. We can control the output voltages of the two DACs by the keyboard arrows; thus the two DACs act actually as programmable voltage sources...

... The computer measures continuously the three voltages (VIN1, VIN2 and VIN3) and draws three voltage bars whose length is proportional to the voltage magnitudes. Finally, it connects them with a line representing the envelope of the voltage diagram."

Another but shorter movie of the screen: photos.app.goo.gl/9UsAnnU9ymeZkBn39. Do you see any connection between this geometrical interpretation and the Bob Duhamel's "video using a ruler with a lady"?

And something very interesting in CD - electrical.codidact.com/questions/279860 where I was punished with -1 instead of being rewarded for what I reported...

@Circuitfantasist Ah yes, the short movie is good to complement the Wikibook discussion. However, there is not subtitle in words or speech with it, so that is not very helpful, comparing with Bob Duhamel.

Nice song...

OK... Only to note the long movie is better since it shows all the possible combinations between the voltages...

By the way, I just finished the first data conversion part of my rpi4 thonny python, declarative, newbie proof, tunnel diode I-V curve matplotlib plotting function. Will show you after my locking jog and supper. See you later. Cheers.

Did I miss something? Do you mean the long WikiBook discussion with the pretty young lady? But there is no subtitle or comments, or PC programming. :) Anyway, I need to go. See you late this evening or tomorrow.

And if you use matplotlib, you can do animated GIF, user interactive interface. This is what I am trying to do next, plotting the tunnel diode I-V curve as animated pictures.

I meant my movie showing a "living voltage diagram" on the screen of Apple II... It gives a very good notion about the R1-R2 network that is widely used in op-amp circuits... BTW, in the early 90s, I was interested in TURBOPASCAL. Then I made a similar attractive experiment - "living load line". It was implemented on the base of a data acquisition system inside an IBM PC. I have printed screenshots.

Maybe, my answer would be interesting for you?