Op amp amplifier with capacitor
Let's look at specific cases. Start with a standard inverting op amp.







simulate this circuit &ndash; Schematic created using CircuitLab

If Vin is a DC voltage, the output will be a DC voltage with (approximately) Vout = -(R2/R1)Vin. The same holds true (approximately) for low-frequency AC signals, where "low-frequency" depends on the op amp.

Now let's try







simulate this circuit

In this case, the effect of bias currents on the input become critical. Every real amplifier will either sink or source small currents at its inputs. For the + input, this is not a problem, since it goes to ground. For the - input, though, the current has no place to go, and will slowly charge up the capacitor, and cause the input voltage (+ input minus - input) to ramp up. The result is that the output will ramp up or down and quite quickly saturate at the upper or lower bounds of the op amp's capability.

In the case of ideal inductors, it gets a bit trickier, but not any better. An ideal inductor has zero resistance, so the "obvious" response for DC input is zero volts output. For AC, the circuit ought to work more or less like a resistor circuit, with the gain set by the ratio of the inductor values, where Z = 2 pi L. However, given the phase shift associated with the inductors will almost certainly cause the op amp to break into oscillation.