Because in the leading load or capacitive load the armature reaction is magnetizing.Here the stator flux adds up rotor flux and so the net flux of alternator increases and the net flux produces alternator's voltage.Hence the alternator's voltage rises.

flux the capacitor

Here is A Simple answer for this question

as you know that emf is induced in the conductor when there is change of flux linkage to the conductor which gives rise to the inducement of electric field in the conductor that provide drift velocity to the electrons hence emf is induced in the conductor but the last only till the change in flux in progress and becomes zero as soon as the flux linkages becomes constant hence we summaraize that for inducement of current there must be change in change of flux hence change in electric field that gives rise to allternating emf.

i) leakage flux is those flux which goes through the air and linkage flux is those flux whose go through the cell.

ii)leakage flux is the loss at flux but linkage flu is warning flux.

iii)leakage flux is cause of eddy current loss and linkage flux is case of copper loss.

Flux