Output impedance of an op amp

[Kimly]

I know it is small - but why? I thought it is linked to stage 3 gain, but I thought as a current limiter, it will add to output impedance?

Thanks in advance

[Jerry]

Idealy the output impediance is zero.  You should take a look at the internal circuity of an op amp to see this.  Look at the diagram below.  Look at the right hand side of it where the output section is.  In an ideal world if we had two inputs to our op amp which were exactly the same then we would get zero for the output.  There would be no difference voltage to amplify, which is what the op amp does.  So, if we had zero at our output which is between a positive voltage source and a negative voltage source.  This zero volts would escentially act like ground for the two voltage sources and ground, as we know, is zero ohms.  So we effectively have zero ohms as our output impediance for the op amp.