In which of the following motors, the stator and rotor magnetic fields rotate at the same speed?

In all machine stator and rotor magnetic field rotates (stationary with respect to each other) at synchronous speed with respect to stationary observer.

The bus bar zone faults are generally

Bulk power transmission over long HVDC lines are preferred on account of

The purpose of skewing of rotor slots in an induction motor is

For reduction of harmonics method is given below:
Chording
integral slot winding
skewing
larger air gap
Sr≠Ss : avoid cogging
Sr-Ss≠P,2P,5P avoid synchronous cusps
Sr -Ss ≠ 3P avoid magnetic locking
here, Sr is number of rotor slot, Ss is number of stator slot

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

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%