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diff --git a/3760/CH4/EX4.21/Ex4_21.sce b/3760/CH4/EX4.21/Ex4_21.sce
new file mode 100644
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+clc;
+Vrated=30;//rated output voltage of generater
+Irated=200;//rated output current of generator
+Ra=0.03;//armature resistance(including brushes)
+Rf=2.4;//field winding resistance
+//No-load saturation curve at 2200rpm
+If=[2 4 6 8 10 12];
+Ea=[15 27 35 40 43 45];
+plot(If,Ea);//magnetization curve at 2200 rpm
+
+
+//(1)AT 2200 rpm
+//at no load
+Ea1=28;//induced voltage in armature
+//for this voltage, the field current required, from magnetization curve is-
+If1=4.23;//field current in ampere
+Rt1=Ea1/If1;//total shunt field resistance
+Re=Rt1-Rf;//external resistance
+
+//at full load
+Ea1_=28+Irated*Ra;//induced voltage in armature
+//for this voltage, the field current required, from magnetization curve is-
+If1_=5.67;//field current
+Rt1_=Ea1/If1_;//total shunt field resistance
+Re_=Rt1_-Rf;//external resistance
+
+
+//(2)AT 4500 rpm
+//at no load
+Ea2__=28;//induced voltage in armature at 4500 rpm
+Ea2=28*(2200/4500);//Ea at 2200 rpm
+//for this voltage, the field current required, from magnetization curve is-
+If2=1.833;//field current in ampere
+Rt2=Ea2__/If2;//total shunt field resistance
+Re__=Rt2-Rf;//external resistance
+
+//at full load
+Ea2___=28+Irated*Ra;//induced voltage in armature at 4500 rpm
+Ea2_=34*(2200/4500);//Ea at 4500 rpm
+//for this voltage, the field current required, from magnetization curve is-
+If2_=2.17;//field current
+Rt2_=Ea2__/If2_;//total shunt field resistance
+Re___=Rt2_-Rf;//external resistance
+Pmax=If1_*If1_*min(Re,Re_,Re__,Re___);
+printf('The minimum & maximum value of external resistance is %f & %fohm respectively.\nMaximum power dissipated through rheostat is %f ohm.',min(Re,Re_,Re__,Re___),max(Re,Re_,Re__,Re___),Pmax);
+