example 4.3   
 
 induction motor is to be run at 1440 rpm   
frequency=50 
 when P=2   
Syhchronous speed,Ns=3000 
 
 when P=4   
Syhchronous speed,Ns=1500 
 
 speed of rotor(1440) is less than synchronous speed 1500, therefore P=4\n   

slip is 4 percent and number of poles is 4 