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+// chapter 9
+// example 9.4
+// find the electrical conductivity and resistivity of germanium
+// page 273
+clear;
+clc;
+// given
+ne=2.5E19; // in /m^3 (electron  density)
+nh=2.5E19; // in /m^3 (hole density)
+ue=0.36; // in m^2/(V-s) (electron mobilities)
+uh=0.17; // in m^2/(V-s) (hole mobilities)
+e=1.6E-19; // in C (charge of electron)
+// calculate
+// since ne=nh=ni,  therefore we have 
+ni=nh;
+sigma=ni*e*(ue+uh); // calculation of conductivity
+printf('\nThe conductivity of germanium is  %.2f /ohm-m',sigma);
+rho=1/sigma; // calculation of resistivity
+printf('\nThe resistivity of germanium is  %.2f ohm-m',rho);
+// Note:  In the question, the value of ni has been misprinted as 2.5E-19 /m^3 rather it should be 2.5E19 /m^3. I have used 2.5E19 /m^3
+
+