1. if the peak amplitudes of waves in case of full wave rectifier are not equal, what could be the reason?

2. in case of full wave rectifier with zener diode why does poor regulation of some I(current through the load resistance) occur?

1. The voltage dropped across the

diodes might not be equal or the
voltages from the center-tapped transformer might not be equal.
Therefore, you could have a defective transformer or diode.

2.In cases where there are large variations in the input voltage and the load, a zener diode and series resistor are insufficient.