I was wondering... I have read about ideal op amp, that we could change this circuit :
Into this one (with the ideal model), where the input resistance Ri is infinite, and the output resistance negligible (so Ro = 0 Ohm) :
We then told me that, since the Ri is infinite, the voltage at node A is zero (since Vi = 0), so Va = 0 (node voltage).
But what happens if we have that?
Will the voltage at A still be zero? Does it changes absolutely nothing to have Vs2 there? I'm confused on this one. I've seen only problems with the + gate of the op amp at ground.