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In the derivation for the gain of a summing amplifier, I have labelled nodes 1 and 2 as being 2 separate nodes. Is this correct? or do points 1 and 2 count as 1 overall node?

(Points 1 and 2 are the points circled)

Thanks in advance

  • $\begingroup$ Whether or not this labeling is "correct" depends entirely on why you used these labels and what you intend to do next. $\endgroup$ Apr 26, 2022 at 10:17
  • $\begingroup$ You would then need an additional equation, viz; V_2 = V_1. $\endgroup$
    – AJN
    Apr 26, 2022 at 13:08
  • $\begingroup$ One overall node, but as comments have indicated, they can be separated to place emphasis on the high impedance negative terminal of op-amp, where I- = 0 and I3 = I4. $\endgroup$ Apr 26, 2022 at 19:26

1 Answer 1


They are the same node. You could slide them together and there would be no difference in the circuit. Use whichever format makes analysis easier.

  • $\begingroup$ While you are correct, I can see useful pedagogical reasons for separating the single electrical node into two halves. It looks like someone is trying to emphasize i3. $\endgroup$ Apr 26, 2022 at 10:18

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