Answer / doss

actually there is both positive and negative voltage occurs in the phase(phase line) with respect to the neutral line. this speed of positive and negative voltage variation is purely depends on the frequency of the ac supply. that is during positive half cycle of ac supply the phase line is positive with respect to the netral line. and during the negative half cycle of ac supply the phase line is having a negative voltage with respect to the neutral line(i.e. neutral is positive voltage with respect to the phase line during negative half cycle of ac supply). so we cannot define positive and negative terminal in case of ac supply since the same terminal can act as positive in one half cycle and during other half cycle the same terminal act as negative. so we simply say it as phase and neutral.

Answer / surendra

load safty is responsible for all these classification.. as
in case of dc there is a permanent neutral.. in ac there
should be a neutral.so that more variation in voltage we can
get..and load can get reliable voltage .........

Answer / ramkumar

in ac we will be getting supply only in one terminal which
is called phase. in neutral there is no power supply. the
general meaning of neutral itself nothing... but in case of
dc we will be getting supply in both the terminals. one as
positive and one as negative.

Answer / samarpal singh

No polarity in A.c

What is the pratically meaning of neagative going ac current.

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