CBSE Class 12-science Answered

It is electrically the same as having two separate secondary coils, of equal 
turns each, wired in series so their AC voltages add up.

Often the transformer is used with the center-tap connected to the 
"ground" or "common" or otherwise zero voltage point in the circuit being 
powered.
So, when listing the voltages on each of several taps on a long coil, one 
of the taps will be labeled "0",
and each other will be labeled with the AC voltage it has with respect to 
the "0" tap.