explain phasors and phasor diagram.......

Phasor is a vector that represents a sinusoidally varying current and/or voltage whose time period, amplitude and angular velocity are time dependent.

A phasor diagram is drawn to show the phasor relationship between voltage and current in an AC circuit.

The phasor diagram is drawn corresponding to time zero along the horizontal axis. The lengths of the phasors are proportional to the values of the voltage and the current at the instant in time. From the diagram we can easily find out whether the current and voltage are in phase or one of them is lagging behind.