according to theory of ac the polarity changes so if we connect the +ve terminal of the motor to the one terminal of the ac source then this +ve terminal of motor always connects to the +ve or be -ve according to frequency. ?

 

No. If it is an AC motor it would not (I reason) have polarized terminals.

 

AC - Alternating Current. With AC there is no constant + and -
Polarity rate changes at the frequency of the supply!
Max.

 

but if the polarity changes according to supply frequency then for positive half cycle its rotete in one direction and for negative half cycle it will rotate in opposite direction ....
but this is not happened in real ...
so how can we apply theory of ac????

 

Click thru this presentation.

https://www.wisc-online.com/learn/career-clusters/stem/iau12708/motor-action

 

but if the polarity changes according to supply frequency then for positive half cycle its rotete in one direction and for negative half cycle it will rotate in opposite direction ....
but this is not happened in real ...

The motor doesn't reverse direction when the current reverses because, in an AC induction motor, both the rotor and stator currents reverse at the same time, thus keeping the magnetic rotational force in the same direction.
Perhaps this will help.

 

Think of an AC induction motor as a shorted turn transformer at switch on, which essentially it is, the high currents induced in the shorted turn secondary (rotor) bars produce a magnetic field, just as it does in a normal transformer, the field produced, creates a magnetic field in the rotor which attempts follow the rotating field in the stator.
The rotor rpm increases to the point where the rotor almost catches up with the stator field, but in a asynchronous induction motor it can never achieve synchronism as there would be zero induced current in the rotor.
So it lags the frequency of rotation by a small number of rpm dependent on load, known as slip frequency.
There are AC motors where there are features added in order to make it synchronous.
Max.

 

Click thru this presentation.

https://www.wisc-online.com/learn/career-clusters/stem/iau12708/motor-action

thanx for this nice thing...
and please say if there are any other website like this which can help to understand this type of electrical things....

 

thanx you all..

i just asked what i want to asked through the example of motor but my real question is somehow different

according to the theory in ac polarity changes ,
so in the electrical socket provide in our house is the live wire becomes nutural and nutural becomes live alternately with supply frequency?

AND IF NOT THEN WHAT IT MEANT BY IN AC POLARITY CHANGES AND HOW WE IMPLIES IN THINGS LIKE THIS SOCKET?

 

The neutral is always neutral, just the polarity alternates between the two conductors, the is no other significant difference between the two conductors, in a single phase system (non-star point), neutral can be decided arbitrarily between conductors.
Ground Practices
Max.

 

so in the electrical socket provide in our house is the live wire becomes nutural and nutural becomes live alternately with supply frequency

No.
Neutral is always zero volts with respect to earth ground.
The voltage at the live wire just goes plus and minus around with respect to neutral at the alternating frequency.

 

No.
Neutral is always zero volts with respect to earth ground.

Although... neutral may not always be at earth ground potential, single phase obtained by a 3 phase transformer as it is in the U.K. and elsewhere is one phase and the star (neutral) point of a 3ph transformer, which in the case of most service suppliers IS connected to earth, but not always in local applications.
Max.