Question

can someone explain the concepts of ac circuit. medal and fan

Answer 1

effective voltage and current, peak voltage and current, reactance, impendance,etc

Answer 2

Check out this link for basic concepts of AC itself. http://www.allaboutcircuits.com/vol_2/chpt_1/1.html
This link about reactance the opposition to AC: http://www.allaboutcircuits.com/vol_2/chpt_4/2.html
and http://www.electronics-tutorials.ws/accircuits/ac-inductance.html
This link for the different ways to measure AC: http://www.electronics-tutorials.ws/accircuits/ac-inductance.html and http://www.allaboutcircuits.com/worksheets/rms.html

As you can see you have asked for lot of information, here is a link on impedance which is the complex value of resistance and reactance. http://whatis.techtarget.com/definition/impedance This is a considerable amount of information, but take your time studying it and you will get a good handle on AC.