a four pole, series motor runs at 900rev/min when taking 30A from a 230V supply. the total resistance ofthe armature and the series field is 0.8Ω. Calculate the additional series resistance required to reduce the speed to 500rev/min if the torque developed is:
i) constant?
ii) proportional to speed?
iii) proportional to the square of the speed.
(Assume the magnetic circuits is unsaturated.)