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+// Implementation of example 7.2
+// Basic and Applied Thermodynamics by P.K.Nag
+
+clc
+clear
+
+// T for temperature,m for mass,S for entropy,dS is change in entropy
+t1=273 // K
+t2=373 // K
+m=1 // kg
+c=4.187
+// (a)
+dSw=m*c*log(t2/t1);
+// reservoir's temperature remains constant so dS=Q/T
+Q=m*c*(t2-t1);
+dSr=-(Q/t2);
+dSu=dSw+dSr;
+printf("entropy change of universe = %.3f kJ/K \n",dSu);
+// (b)
+// now water is heated in stages from two reservoirs..
+t3=323 // K
+dSw=m*c*log(t3/t1)+m*c*log(t2/t3);
+dSr1=-[m*c*(t3-t1)/t3];
+dSr2=-[m*c*(t2-t3)/t2];
+dSu2=dSw+dSr1+dSr2;
+printf("entropy change of universe in 2nd case = %.3f kJ/K \n",dSu2);
+// the entropy change of  universe would be less & less if water is heated in more & more stages...it will be zero if water is heated reversibly...
+// end
+\ No newline at end of file