4- A DC motor (separately-excited) chopper controlled and is considered for low-speed applications, with Vs is 400 V, and requiring less than 4 % pulsating torque at 300 rpm. 4Hp, 220V, 1800rpm, R₁ = 0.77 Ohms, Kb =0.9, La = 0.011, d= 0.3, Fc = 300 Hz. E=130 V. == a- Find Tej? b- Find Ter?