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diff --git a/3760/CH4/EX4.20/Ex4_20.sce b/3760/CH4/EX4.20/Ex4_20.sce
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+clc;
+ra=0.5; // armature resistance
+rf=180; // shunt field resistance
+n=1100; // speed at which generator is being driven
+n1=1000; // speed for which data is given
+disp('case a');
+// from the data given in question magnetising curve is drawn (fig 4.46)
+If=[ 0 0.2 0.4 0.6 0.8 1 1.2 1.4 ];
+Ea=[5 50 100 140 170 190 200 205];
+Ean=(n/n1)*Ea
+plot(If,Ean);
+xlabel('field current');
+ylabel('generated EMF');
+title('Magnetising curve for n=1100');
+// line corresponding to rf=180 ohms to meet saturation curve at 221 V which is no load EMF
+Eo=221;
+printf('No load EMF is %f V\n',Eo);
+disp('case b');
+vt=190; // terminal voltage
+// from curve armature resistance drop is given by line BC
+vd=22.5; // armature resistance drop
+ia=vd/ra; // armature current
+ifl=vt/rf; // field current
+printf('Shunt field current is %f A\n',ifl);
+printf('Output current is %f A\n',ia-ifl);
+disp('case c');
+// OP represents maximum armature resistance drop i.e OP=46.5 V
+vd=46.5; 
+ia=vd/ra; // armature resistance
+// tangent point at R gives field current which is
+ifl=0.635; 
+printf('Maximum output current is %f A',ia-ifl);
+disp('case d');
+// under steady state short circuit terminal voltage=0 V and residual flux EMF is
+E=5.5; // residual flux EMF
+printf('Steady state short circuit current is %f A\n',E/ra);
+disp('case e');
+Eo=210; // no load voltage
+// for Eo OD represents field resistance field current is 1.015
+ifl=1.015; // field current
+rfn=Eo/ifl; // field resistance
+printf('Additional resistance required is %f ohms\n',rfn-rf);
+disp('case f');
+rf=150; // shunt field resistance
+vt=180; // terminal voltage
+p=0.04; // reduction in flux due to armature reaction
+ifl=vt/rf; // field current
+Ea=220*(1-p); // generated voltage
+ia=(Ea-vt)/ra; // armature current 
+il=ia-ifl; // load current
+printf('Load power is %f KW',(vt*il)/1000);