Question

When will the potential difference between the input terminals of an op-amp is treated nearly to zero?

Answer 1

➡When the op amp is in its linear region (i.e. its output is not at one of the rails), then the voltage across the input will be very low. In many applications this can be effectively treated as zero. The reason is that the gain of an op amp may be around 10 thousand so a 1 volt change in output is effectively 100 microvolt across the input. That’s under steady state conditions or low frequencies.