from wt: 0 to , output voltage will follow input voltage, hence Vo= eg
from wt: pi to 2, output voltage will double the input voltage, hence Vo=2eg
The concept is that-- "Current always flows from positive to negative terminal if and only if diode is forward biased"
Still if you have problem you can ask me in comment section.
The circuit below uses a transformer with center tap access, which feeds a six-diode rectifier The voltages v, and v2 have the same amplitude and are 180 electrical degrees shifted from each other...