The Five True Lies of the Operational Amplifier

The electronic engineering world is built on five statements about their favorite device - the operational amplifier (op-amp). None of these statements is really exactly true but we all make like they are true and it all works out fine anyway (most of the time).
 

1. An op-amp has infinite input impedance.
2. An op-amp has zero output impedance.
3. An op-amp has infinite gain.
4. An op-amp has infinite bandwidth.
5. The voltage difference between the + and - inputs  of an op-amp is zero.