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+//CHAPTER 8- DIRECT CURRENT MACHINES
+//Example 4
+
+disp("CHAPTER 8");
+disp("EXAMPLE 4");
+
+//VARIABLE INITIALIZATION
+v_t=240;                   //in Volts
+I_l=200;                   //full load current in Amperes
+r_f=60;                    //shunt field resisatnce in Ohms
+eff=90;                    //percentage full load efficiency
+s_loss=800;                //stray(iron + friction) loss in Watts
+
+//SOLUTION
+
+//solution (a)
+p_o=v_t*I_l;               //output
+eff=eff/100;
+p_i=p_o/eff;
+tot_loss=p_i-p_o;          //since input=output+loss
+I_f=v_t/r_f;
+I_a=I_l+I_f;
+cu_loss=(I_f^2)*r_f;       //copper loss
+c_loss=cu_loss+s_loss;     //constant loss
+arm_loss=tot_loss-c_loss;  //armature loss ((I_a^2)*r_a)
+r_a=arm_loss/(I_a^2);
+disp(sprintf("(a) The armature resisatnce is %f Ω",r_a));
+
+//solution (b)
+//for maximum efficiency, armature loss = constant loss =>(I_a^2)*r_a=c_loss
+I_a=sqrt(c_loss/r_a);
+disp(sprintf("(b) The load current corresponding to maximum efficiency is %f A",I_a));
+
+//END