why does gain decrease as frequency increases for an operational amplifier?

Question

A signal from a function generator is inputted into the circuit and as frequency increases the gain decreased and a phase shift was observed between the output and input. Anyone have an explanation as to why this happens.

Answer 1

If you're only looking at the op-amp characteristics, there is normally a pole intentionally designed into them for stability reasons. This way, the gain will be less than one when the phase reaches 180 degrees. Without this, the op-amp would oscillate. Do an internet search on phase margin or gain margin for more information.

Answer 2

The gain of the amplifier is rolling off with freqyency. It's like driving an RC network