Voltages at Secondary Winding in Centre Tap Full wave rectifier
How it possible to have the same voltage as the input [on only half of the secondary]?


To achieve this the manufacturer would put twice as many turns on the secondary.

Since each half of the transformer secondary is only used on alternate half-cycles the wire rating only needs to be half the capacity of a full-wave rectified single-coil secondary. In effect the weight of the copper would be the same for a single-coil full-wave PSU or a split-coil double half-wave PSU. Similarly the same laminations could be used for either as the power requirement is the same.