Thank you for the answer!
To clarify:
1. On what external "components" would the slew rate of the op-amp depend upon?In what conditions, diode will affect the slew rate? Junction capacitance of the diode?
2. Also, if I increase the length of the output of the op-amp signal line (say I connect the output of op-amp to a cable), the slew rate will get impacted for the worse, right?
Well I think it is time we started to outline the clear difference between the op amp slew rate specification SR and the circuit "slew rate" which I think would be better thought of as the circuit response (CR).
The SR is really not changeable. That's because it is how the op amp itself behaves without any circuitry connected yet.
The CR is completely changeable and this should be obvious because different electrical parts have different characteristics of their own, such as inductors and capacitors. For a simple example, say we connect the output of an op amp with SR around 10v/us to the input of an op amp with an SR of only 1v/us. The output of the second op amp is only going to slew at 1v/us even though the first one is able to slew at 10v/us, and thus we altered the slew rate of the first op amp with the second op amp.
A more typical setup though is to create a filter of some kind. In that case, the slew will be limited to whatever the added circuit does, not the op amp, provided the op amp selection fit the application decently to begin with.
Now maybe we can talk about the questions 1 and 2.
[1]
Any components with a reactive element such as a capacitor or inductor may alter the CR but it would not alter the SR because again, the SR is a specification of the op amp itself. If we connected a capacitor from the output to ground that could make the SR look slower, but that would really still be part of the circuit response CR because then we no longer have JUST an op amp we have an entire circuit, even though it's a small circuit.
A diode, with internal capacitance, may or may not alter the CR (it does not alter the SR) depending on how fast the op amp is. If the op amp is a general purpose 0.5v/us SR op amp, a diode probably is not going to affect it much. If the op amp had a very fast slew rate spec, then the diode capacitance could alter the CR somewhat. It depends on the op amp slew rate, the drive capability, and the diode.
[2]
If you increase the cable length on the output of the op amp, or even use a short cable, then we have to look at transmission line effects, and that could have a massive impact on the CR when you go to measure the output of the cable, and it may even have an impact on the input to the cable, but that would still be considered the CR not the SR.
In short, the SR comes with the op amp and pretty much stays the same all the time. The CR depends on circuit components and can therefore vary widely, and possibly make the op amp output itself look slower depending on how it loads the op amp.
The input can also have an effect on the CR of course because there could be reactive components there too. Now the output of the op amp may appear to slew much slower, but that's not due to the op amp itself it is due to the components connected to the input. Maybe we could call this the "apparent slew rate" but it's just part of the CR really, and the SR of the op amp itself did not change.
This is just like anything else. When we look at one component by itself it had certain characteristics, then when we connect it to other components we see some different responses come about. That does not mean that that one component changed itself. It still, usually, maintains its own behavior it is just that the circuit response changes due to the mix of parts.