Why is the output impedance of a non-inverting op amp zero?
Why is the output impedance of a non-inverting op amp zero?

It is about the so-called &quot;differential output impedance&quot; that is the ratio of voltage and current changes - dRout = dVout/dIout.
There is a voltage-type negative feedback in this circuit that makes the op-amp keep a constant output voltage when the output current changes (the op-amp output behaves as an &quot;ideal&quot; voltage source). So the ratio is almost zero.