Why An AC cycle is 360 degrees, with the first 180 degrees positive and the next 180 degrees negative. A half-wave rectifier uses a single diode that conducts only when the input polarity forward-biases it, so only one half of each cycle, 180 degrees, reaches the output; the other half is blocked. That is why a half-wave supply has a low, ripply output that needs heavy filtering.
Watch out The choice of 360 degrees describes a full-wave rectifier, which flips the other half cycle instead of discarding it, so the whole cycle contributes to the DC output.
Half of 360 is 180: half-wave = 180 degrees, full-wave = 360 degrees.