It isn't majic. It is the frequency where the reactance of the 10uF capacitor equals the 1k resistor and at that frequency the response is down -3dB for each opamp.aibelectronics said:
No. The DC input offset voltage for a more expensive LM324A is typically only 2mV and is 3mV max. The DC input offset voltage for an inexpensive ordinary LM324 is also typically only 2mV and is 7mV max.
You might need to test through a bucket full of opamps to find a "typical" one and hope that the company who bought thousands before you came along didn't take all the best ones.
Even if you found an opamp with only 2mV for its DC input offset voltage then its output will also be welded to a supply rail if the opamps were DC-coupled.
