N s is the synchronous speed. N shaft rotation speed revmin rpm f frequency of electrical power supply Hz cyclessec 1s p number of poles. Hence speed of a DC motor is directly proportional to emf of rotation E and inversely proportional to flux per pole f.
Slip of a motor can be found from the formula.
For a 50-Hz system the formula would be. Slip of a motor can be found from the formula. O angular speed measured in radians per second rads. The above relation shows that the speed of a DC motor can be controlled through change in voltage flux and armature resistance.