Efficiency= output power/input power
efficiency = (v*i*cosφ)/((v*i*cosφ)+(x² Pc)+(Pi)) x=fractional part of full load
Ns = 120f/P
Ns = 1000 and Nr = 960
from equation of slip, S = (1000-960)/1000
S = 0.04 or 4%
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.