Recently we have been working with opamps in the lab and I never can understand how to determin the output and input impedance of a circuit with op-amps (not the input and output inpedance of the circuit itself)
We have been measuring it by placing a voltage signal in the output of an inverting amplifier with its imputs grounded. Measuring the voltage over an impedance we have found the current flowing in
Then the output impedance is found to be the voltage at the output (Vout) divided by the current.
I would like to know what the input and output resistances in opamp circuits represent and if possible how to obtain them from equations