what are the applicatons of op amp in signal processing?
But how op-amp can be useful in signal processing application?


Op-amps are the standard building block of many analogue circuits. They can be used to make many circuits like:


Inverting, non inverting, buffer and differential amplifier.
Analogue adder and subtractor.
Active filter: high-pass, low-pass, band pass.
Differentiator and integrator.
Current to voltage converter.
Negative resistor
Peak detector
Analog multipliers (by using log and antilog amps)
Gyrators (effectively an inductance made from opamps and capacitors and often a very large inductance value)
Different types for different applications


(I'll leave this open for community so you can all add your favorite op-amp application)