Due to skin effect

Skin Effect:
tendency of the current to crowd near the conductor surface.

Skin effect is proportional to frequency, conductor diameter and permiability.
Skin effect increases effective resistance of conductor.
In DC, no skin effect.

The form factor in AC means the ration of

A 3 phase, 6 pole induction motor operates on 440 V, 50 Hz, supply. If the actual speed of the motor is 960 rpm the slip will be

Ns = 120f/P
Slip=(Ns-Nr)/Ns
Ns = 1000 and Nr = 960
from equation of slip, S = (1000-960)/1000
S = 0.04 or 4%

Fot fast load flow calculations, the best method is

In a series RLC circuit at resonance

The picture on the monitor of a computer is made up of tiny coloured dots called