A separately excited DC motor rated at 5 kW and 2500 rpm has an armature resistance of 1.5 N. At rated conditions, the armature is fed at rated armature voltage and current of 400 V and 14.4 A respectively. The field winding is fed at rated field voltage and current of 250 V and 1.2 A respectively. The rotational losses are negligible. [4 marks] (a) Determine back-EMF of the motor when the motor is delivering rated power at rated speed. (6 marks) (b) Determine the armature terminal voltage required to deliver rated output power at half the rated speed (1250 rpm). (c) Calculate the motor efficiency at rated conditions. [5 marks]