For a half-wave rectifier, the time Tp corresponds to a full period (not a half period)
of the signal, so the factor 2 does not appear in Equation (2.9). The factor of 2
shows that the full-wave rectifier has half the ripple voltage of the half-wave rectifier.
Equation (2.9) can be used to determine the capacitor value required for a particular
ripple voltage.