[2] An OP amp can be an ideal amp, if used at infinite gain and bandwidth if used in the open-loop mode via usual DC gains of well over 100,000 or 100dB. An ideal OP amp also has a 0 output impedance.
It works from either a dual positive (+V) and an corresponding negative (-V) supply, or they can work from 1 DC supply voltage.
An OP amp's 2 main laws is that it has an infinite input impedance (Z = ∞) resulting in no current in its 2 inputs and 0 input offset voltage V1 = V2.
Closing the open-loop by connecting a resistive or reactive component between the output and one input terminal of the op-amp greatly reduces and controls this open-loop gain.
An OP amp's output voltage is: Vout = A(V+ + -V-) or V+ - V- for short
[S1] An OP amp's negative is the inverting input. If a signal used to inverting input, the output signal is 180° out of phase to it.
An OP amp's positive input is the non-inverting input. If a signal used to non-inverting input, the output signal is 180° in of phase to it
Any difference of V+ and V- yields a very big output
An OP‑amp in open loop is a difference detector with enormous gain. That’s why we almost never use OP‑amps open‑loop, but negative feedback to control the gain and make a circuit stable and predictable
