Why is the voltage gain of an open loop circuit of an op-amp dependent upon the frequency of the signal?

 

Hi aragon
This link explains the reason.
Note the Open Loop Gain plot
E
https://www.electronics-notes.com/a...erational-amplifier-op-amp/gain-equations.php

 

Why is the voltage gain of an open loop circuit of an op-amp dependent upon the frequency of the signal?

Also the voltage gain of an opamp with feedback is frequency-dependent.
More than that - the gain for each amplifier (integrated or discrete) will depend on the signal frequency.
This cannot be avoided because each circuit (even a simple resistive voltage divider) contains hidden capacitive effects which cause a amplitude reduction for rising frequencies (can be observed sometimes in the high MHz region only)